[Issuedwith4r~nyOrdersfOr January.1927

7°PE.

of the

HeightandRangemFinder,No. 2MARK II

TYPE U.B. 2(BARR & STROUD)

1927

I

ILONDON:

PUBLISHED BY HIS MAJESTY’S STATIONERY OPPICE.Tobepurchased directly from H.M. STATIONERY OPPICE at thefollowing addresses:

AdastralHoute,Klng!way, London,W.C. 2; zzo~GeorgeStreet,Edinburgh;York Street,Manchester;e, St.Andrew a Crescent,Cardiff;

x~,Donegall SquareWest, Belfast,orthroughanyBookseller.

*927

Price is. Od. Net.

HANDBOO’

[Issuedwith ArmyOrdersfor January,1927’

-~P.F.

HANDBOOK’~~~iAY1~33O~’).:~\ ‘~ //

of the

Height and Range-Finder,No. 2MARK II

TYPE U.B. 2(BARR & STROUD)

1927

By Commandof tha Army Council,

THE WAR OFFICE,

13th Januarl’, 1927.

- LONDON:PUBLISHED BY HIS MAJESTY’S STATIONERY OFFICE.

To be gurchased‘directly from H.M. STATIONERY OFFICE at the following addresses:Adastral House, Kingsway, London, W.C.z; tao, George Street, Edinburgh;

York Street, Manchester;i, St. Andrew’s Crescent, Cardiff;55, DonegallSquareWest, l3elf ass;

or through any Bookseller.

5927

Price is. Od, Net.

CONTENTS.

PAGE

INSTRUMENT DATA ... ... ... 3

CHAPTER I

PRINCIPLES AND THEORY OF THE HEIGHT AND RANGE.FINDFR ... 5Introductorynote. Range-findingprinciple. Coincidenceprinciple. Height-finding principle. Application of theaboveprinciplesto theheight andrange-finder.

CHAPTER II

DESCRIPTION OF TIlE HEIGHT AND RANGE-FINDER AND ADJUNCTS... 15Introductory note. External arrangements.The stand,mounting and illuminating gear. The height scale gear.Internal arrangements. The lath, adjusting. The case.Careand preservation. -

CHAPTER III

TESTING AND ADJUSTING ... ... ... ... ... ... 28Introductory note. Halving adjustment. Coincidencead-justment. Use of the lath, adjusting. Alignment of view-finder. Adjustment of slip bearings.

CHAPTER IV

DRILL FOR TIlE HEIGHT AND RANGE-FINDER No. 2, Mi~.II, TYPE

U.B.2. .., ... ... ... ,.. ... 35

- CHAPTER V

NOTES ON TIlE TRAINING OF HEIGHT-TAKERS ... ... ... - ... 39

APPENDICES

I. Theoryof coincidencerange-findingandheight-finding ... ... 42Tablesof permissibleerrors... ... ... ... ... ... 42Theoryof thelath,adjusting ... ... ... . .~ ... 42

II. Adjustmentsandrepairswhichmay beundertakenby ArtificersR.A., who havepassedacoursein Anti-aircraft instruments 52

INDEX ... ... ... ... ... 55

.2

INSTRUMENT DATADimensions

Overall lengthof instrumentHeightof opticalaxisfromthegroundTripod

Stand, overall height ...

Maximum splaybetweenfeet (measuredfromfootrest to footrest) ...

InstrumentCase ... ... ...

WeightsHeightandrange-finderNo. 2, Mark~II:—

InstrumentCase

Tripod :—

Stand ... ...

Head,mounting ...

Cover, canvas,waterproofProtectors,sun,canvasCover,linen ... ... jLath, adjusting ...

Box, battery,switch andresistancecoil6 Cells, electric, inert “0Totalweightof instrumentand accessories

Coincidence, erect, withinverted strip.

2 metres=6~56feet.15 and 25 diameters

(approx.)10 36’ circular (approx.)±5 dioptersvariation

00 5’ (approx.)View-finder :—

Field of viewMagnification

ModeratingglassesRed,yellow, greenandclear

Scales:—Instrument

InternalrangescaleHeight andrangescales

RangescaleHeightscale

Elevationscale

(Note.—Owingto thenatureof thescalesit is not possibleto constructgearswhich will give correctreadingsoutsidecertain limits. The heightscaleonly givescorrectreadingsfor anglesof sight between10°and 700,andaninstructionplateto this effect is attachedto the instrument).Tripod :—.

Mountingheadazimuthscale

85~25inches

57.5

47.4

34.5

88~75inches longl5~25 ,, wide21~625,, deep

lb. oz.93 10195 oJ

Totals

lb. oz.

188 10

2(3 12)- 59 12

60

4 6~ ~

24 8

283 4~

OpticalInstrument

Type of field

Length of baseMagnification

Field of viewEyepiecefocussingscaleHeightof strip field

6°circular (approx.)6 diameters(approx.)

2,000to 25,000yards

2,000to 12,500yards1,000 to 30,000 feet—3°to-f90°

Graduatedin degrees00 to 360°figured every

10°

3(711) A2

INSTRUMENT DATA—continued.

Adjunctscarried in caseLeathersatchelcontaining:—

Chamoisleather ...

Handkerchiefs,linenScrewdriver ...

Rayshades ... ... ... . . -

Protectors,sun,canvas ... ...

Eyeguards,spare ... ... ...

Cover, canvas,waterproof ... ...

Lath, adjusting,No. 2, height andrange-finderTool, Marie II, No, 2, height andrange-finder

2I2221I1

CHAPTER I

PRINCIPLES AND THEORY OF THE HEIGHTAND RANGE-FINDER

INTRODUCTORY NOTE

i. Theprimary functionof theheightandrange-finderNo. 2,Mark II, is the determinationof heightsand rangesof aerialtargets.

2. The instrument is a coincidencerange-finder, with aninvertedstrip field. As aheight-finderit relies on its measure-mentof theangleof sightto thetargetin additionto its measure-ment of the range. -

3. The following essentialpoints shouldbe noted:—

(a) The range is found by the “coincidence” principle, adescriptionof which will follow.

(b) The baseis self containedin the instrument.(c) Oneobserveronly is requiredfor controlling theessential

operationswhich determinethe range(and,in the caseunder consideration,the height also) though othersmaybe employedfor the purposeof following amovingtarget and readingheightsand ranges.

4. In the last respect it differs essentiallyfrom the typesof instrumentin which two observersmustmakeobservationsat

~i eachendof agiven base. As with all Short baserange-finders,~ the rangeis obtainedindirectly by the measurementof the angle

subtendedat the objectby the baseof the instrument,this anglebeing termedtheparallaxor apexangle.

5. The heightandrange-finderitself forms the actualbaseofa triangle,havingat its apexthe objectwhoseheightandrangeare to be determined. The range is determinedby measuringtheparallaxangle; whilst theheightis computedby mechanicalgearingwhich automaticallycombinesthe measurementsof rangeandangleof sightmadeby the instrumentto give asolutionof thetrigonometricalequationfor height.

6. The base,beingself containedin the instrument,is thuscomparativelyshort, but the “virtual” base in use is muchgreater,being equalto the length of the actualbasemultipliedby the magnifying power of the instrument.

7. The accuracyof the range-findingis directly proportionalto the virtual base. There is, however, a limit both to theactual length of baseand to the magnification wl~iichcan be

5_

convenientlyandusefully employedwith anyparticular type ofinstrument.

8. The accuracyof the height-finding is proportionalto theaccuracyof the range-findingandto the accuracywith which theinstrumentmeasuresthe angleof sight to the target. -

9. The chiefadvantagesof this typeof instrumentover typeswhich employ two observersat oppositeends of a longerbaseare

(a) That only one main observeris required.(b) Its rapidity in use,andin erection.(c) That both ends of the basemust alwaysautomatically

be on the sametarget.(d) That no surveyingof the baseis necessary.(e) That the necessityfor intercommunicationbetweenthe

endsof the baseis eliminated.(f) Comparativelygreateraccuracy,basefor base.

xo. The chief.disadvantagesof this type of instrumentare:—(a) Liability of the accuracyof height andrange-findingto

be affected by the “shimmer” causedby varyingdensityof the air.

(b) Delicacy,anddifficulty of repair in the field.(c) High degreeof trainingrequired.

THE RANGE-FINDING PRINCIPLE

ii. Let 0~02 in Fig. i representthe baseof the height andrange-finder,and let T be a distant object to which the rangehasto be found.

R

IFig. 1.

6

The principle on which the instrument is designed is that theangleT0102 is automaticallymaintainedas a right angle, sothat the range-findingformula is:— -

BTan 0 = 3 R

WhereB is thebaseof the range-finderin feet.

R is the rangein yards.0 is the apexangle.

The rangeR, measuredby this typeof instrumentis alwaysvery great comparedwith the base B, and consequentlytheapexangle is very small. Hence its tangentmay be replacedby its circular or radian measure. The measurementof 0 insecondsis thus given by

C = 206,265-p-- seconds.3R

sincethereare 206,265 secondsin a radian.

PuttingB = 2 metres= 6~6i68feet:—

= 4~~49seconds

in the caseof the instrumentunderconsideration.

Fromthisthefollowing valuesof theparallaxanglefor various

rangesof the instrumentare derived.RANGE PARALLAX ANGLEyards seconds2,000 225~62,100 2l4~85,000 9O~25,100 S8~5

10,000 45~110,100 44~715,000 300815,100 298825,000 1805 -

12. At all rangesthe parallaxangleis sosmall that it needsmost accuratemeasurementfor good range-finding,on whichgoodheight-findingdepends.

13. The accuracyof range-findingin a coinciden~etype ofinstrumentis assumedto be directlyproportionalto the magni-fication M of its telescopic system. Hence the accuracyobtainablewith amagnificationM andabaseB is the sameasthat obtainable from an instrument of base BM with unitmagnification in its telescopicsystem. The quantity BM maybe termedthe “virtual” base.

7

THE COINCIDENCE PRINCIPLE

14. Considertwo cameras,with lenses01 02 of equal focallength, rigidly connectedtogether,so that the axesof the twolensesareparallelas in thediagrammaticFig. 2.

Fig. 2.

15. If thesecamerasbe directedon to an infinitely distantpoint object, such as a star, two imagesof the objectwill beformed at X1 and X2 on the ground-glassscreensSS of therespectivecameras,rays coming from the objectto eachcamerabeingparallel.

i6. Now let the doublecamerabe directedtowatdsan objectT at afinite distance. Two imageswill againbe obtained,andif the camerasbe adjustedso that the imagein the right handcameracoincideswith X1, the angle01X1X2 beinga right angle,the imagein the left handcamerawill havemovedaway fromX2 to someposition Y2. The “displacement”X2Y2 increasesas the rangeto the object decreasesand is an inversemeasureof the range.

17. The above apparatusmay thereforebe consideredas arange—finder,the basebeingthe distancebetweenthe two lenses01 and 02, and an inversescaleof rangescould be engravedbetweenX2 and ‘2~

18. The trianglesY2X202 and 0501T being similar in allrespects:—

xY _02x2x010222~ TO1A constantRange.

8

19. It is evident that the scaleof rangesX2Y2 must be areciprocalone.

20. By introducingtwo reflectorsR1R2, as in Fig. 3, the twoimagesmaybe thrown on asingleground glassscreenSS. Thetwo images X1X2 are now coincident, and the displacementX2Y2 remainsan inversemeasureof the rangeas before.

- 21. By next introducing two right-angled glass prisms Jplacedone abovethe other,the imagesmaybe reflectedon to thescreenSS placed in a position parallel to 0102, as in Fig. 3a. -

The rayssuffer total internalreflection andthe two imagesX1X2areformedcoincident,but oneabovethe other,andareseparatedby a “dividing line.” Once againX2Y2 is the displacementanda measureof the range.

+

Fig. 3a.

/

22. A scaleof rangeson the glassscreenwould, however,betoo small to be convenientlyreadable,and other meansmustthereforebe adoptedin orderto obtain asufficiently largescale.

This is effected by the introductionof a prism P of smallanglein thepathof the rayscoming from R2, as in Fig. 311.

Fig. 3.

9

NrAUTV PQS~TI~,

23. Theprismdeflectstheraysthroughasmallconstantangle.Whenin the “infinity” position,the raysfrom R1 andR2 for aninfinitely distant object are madeto coincide, as before, at apoint X1X2 on the screen SS, one image being immediatelyabove the other. If the instrument is now laid on an objectata finite distance,the two imagesX1 and Y2 will no longerbecoincident,but canbe madeso by moving the prism from P toP1 in the direction towardsR2, as in Fig. 3C.

I~CFLCCT~ACPTASM ~IOVtO~O THE TIFT TOCATA~4 CO4NZ~OEMCE~ A IAPCET AT A FIN~1CR~K.ETp

- Fig. 3c.

24. The distancePP1is ameasureof therangeon avery muchgreater scale than is the displacementX2Y2 of the previousdiagrams.

25. A scaleof rangesengravedon a nickel-silver strip isattachedto the prism which is actuatedthroughgearingby theoperator: this moveslongitudinally,and rangesare readagainstastationaryindex or reader. The scaleof rangesis a reciprocal.one.

26. Thus ranges can be determined by a single observerbringingthe two imagesinto coincidenceby the lateralmovementof the prism P.

27. Strictly speaking,in order to obtain coincidenceon aninfinitely distant object, the prism P would haveto be placedin the planeof the screenSS in Fig. 3, whereit would haveno

Fig. 3b.

10

deflectingeffect. As this is not possiblein practice, the-prismsJareadjusted(bothin relationto eachother,andto their positior.in the planeof triangulation)so that coincidenceof the imagesof infinitely distant objects can be effectedwith the prism Pasnearthe prismsJ ascan convenientlybe arranged-

28. The abovefigures arepurely diagrammatic,the relativedistancesbetweenandproportionsof componentsbeing repre-sented disproportionately,for the purpose of illustrating thecoincidenceprinciple. The prismsJ are of a muchmore com-plicateddesignthanthoseshown,andthepathof the light rayswithin them is more devious.

THE HEIGHT-FINDiNG PRINCIPLE

29. Let T be an aerial target at aheight h feet anda ranger feet from a height andrange-finderA, as -in Fig. 4. Let abe the angleof sightto thetargetfrom the instrument,so thattileheight-findingformula is

ii =rSinaThis equation is solvedautomaticallyby meansof gearing

which is actuatedmechanicallyby the operationsof following atarget andobtainingcoincidence. The gearingis known as the“Height scalegear,” and is attachedexternally to the maintube of the height and range-finder,aboutmidway betweenitsextremities. By taking logarithms the above equationbecomes:—

- Log .T

i = Log r + Log sin a

a form more suitablefor mechanicalsolution. -

Fig. 4.

11

3°.Themain featureof the heightscalegearis adifferentialgear,by meansof which the two quantitieson the right handside of the equationcanbe addedtogether.

APPLICATION OF THE COINCIDENCE AND HEIGhT-FINDINGPRINCIPLES TO THE HEIGHT AND RANGE-FINDER

31. The generaloptical arrangementsof the instrumentareshowndiagrammaticallyin Fig. ~.

32. The various componentsare shown disposedabout theoptical axeswhich areshown as dotted lines.

33. The arrangementsdiffer from thoseshownin the previousdiagramsin the following respects:—

(a) The simple reflectorsR1R2 are replacedby pentagonalprisms placedat the endsof the instrumenttubeandprotected by plane glass windows. Their reflectingsurfacesare silvered.

(11) The two lenses0102now becomethe objectivesof twotelescopeswhich areplacedwith their axescoincidentandpointing in oppositedirectionsoutwardsbetweenthe pentagonals.

(c) The simple pair of right-angledprisms J are replacedby a more complexcombination of prisms called the“centreprism combination.”

(d) The deflectingprism P moveslaterally,asbefore, in theleft-handsideof the instrument,but is reversedin itsaction in formerdiagramsconsequentupon the useofpentagonalprisms in the place of simple reflectors.A nickel-silverreciprocalscaleof rangesQ is attached.to the prismmountandmoveswith it.

(e) The screenSS is eliminated,and the two imagesformedby the two telescopicsystemsand centreprism com-binationareviewedsimultaneouslythroughacommoneyepieceN. It is providedwith two powersof magni-fication, and alsowith various colouredglasses(notshown) which can be thrown into useat will. Theyare for tile purposeof obtaining heightenedcontrastin the field of view under varying atmosphericcon-ditions. A second eyepiece is provided (also notshown) throughwhich the internalrangescalecan beread for adjusting purposes,or when taking rangesabove12,500 yards.

(f) Three other membersare introduced into the opticalsystem :— -

(i) A pair of cylindrical lenses M1M2, one in eachtelescope,which arecalled “astigmatisers.’’ Theyare mounted in hinged mounts and connectedtogether,and, by meansof a lever, can be simul-

12

To fcLa3 page /2.0

.5~__-T’,_ ~

I \ ) I

L~.

p.:

taneously thrown into, or withdrawn from, tileoptical system.

@) A plate of parallelglassL in the right-handtelescopewhich canbe revolvedaboutan axisparallel to theplane of triangulation and at right angles to theoptical axis. It canthusbe setat varying inclina-tions to thelatter. It is calledthe “halvingglass.”

(~)A prism K of smallapexanglewhich is mountedin arotatable circular holder at right angles to theoptical axis of the left-handtelescopebetweentheleft-hand pentagonal prism and the deflectingprism P. It is known as the “coincidenceprism.’’

Tile useof thesethreememberswill be discussedlater.

34. The optical system is achromatic; that is, the maincomponentsareso constructedthat colour defectsare eliminated.

35. The principle on which the range-findingportion of theinstrument works remainsunaltered. If the main observerlays the instrument (which is in correct adjustment) on anobject at a finite range, he will see two partial images of theobject, as in Fig. 6; an erect imagein the top andbottom of thefield of view, formed by the left-handtelescope,andan invertedsmall portion of an image in the narrow strip field which isinterposedhorizontallyacrossthe main field. The imagein thestrip field is formedby the right-handtelescope,and it is at theright-handend of the instrument that tile right angle of therange-findingtriangle is maintained.

36. The junction line betweenthe bottom of the strip fieldand the lower portion of the main field now becomesthe“dividing” line, and it is betweenthepartial imagesaboveandbelowthis line that coincidencemust be made.

37. The inversion of the image in the strip field gives asymmetryof dispositionbetweenthe imageson either sideof thedividing line: this makes lack of coincidencemore readilyperceptible,andimprovestheprobability of accuracyon rapidly

G.e

Fig. 6. Fig. 7.

13

moving targets. Errors in halving (see p. 29) are alsoveryreadilydetected,andgreaterlatitude of heightof imageon whichcoincidencecan be made is obtained. Since an erect imagecanbesecuredin the field of view bothaboveandbelowthestrip,there is lesschanceof the partial imagesentirely disappearinginto the dividing line when the elevationof the instrumentisincorrect than in the caseof anon-striptype of field.

38. The two imagesin Fig. 6, are seento be separated,buttheycanbebroughtinto coincidence,as in Fig. 7, by movingthedeflectingprism by meansof the “working head” which is coxi-venientlysituatedoutsidethe main tube. The workingheadisconnectedthrough a universal jointed coupling to the heightscalegear, which is also connectedto the driving gear of thedeflectingprism, and is furtheractuatedby the movementof theinstrument in elevation. The heightscalegearandthe deflect-ing prism are thusdriven bothby the movementof the workingheadandby the movementof the instrument in elevation.

39. Movementof the deflectingprism causesacorrespondingmovementof the imageacrossthe main field of view. As therange recordedon the rangescalesincreases,the imagemovesfrom right to left and vice versa.

40. In obtainingcoincidence,the height scalegearis auto-matically so actuatedthat it solvesthe height-findingequation.Two externalrevolving circular scalesare driven by this gear:they arereadagainstpointersandregisterheightsfrom i ,ooo to30,000 feet, and rangesfrom 2,000 to 12,500 yardsrespectively.

41. When the images of a target have been brought intocoincidencein the field of view of acorrectlyadjustedinstrument,as in Fig. 7, therangeto thetargetwill beregisteredon therangescales,whilst the heightwill be recordedon the externalheightscale. - -

42. The instrumentis so constructed,that if tile height of atarget remainsconstant,the actof following for elevationkeepsthepartial imagesin coincidencewithout any adjustmentof theworking head.

43. A more detaileddescriptionof the instrumentand its

adjunctswill be found in ChapterII.

14

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CHAPTER II

DESCRIPTION OF THE HEIGHT AND RANGE-FINDERAND ADJUNCTS

INTRODUCTORY NOTE

44. To sumup from the foregoingChapter:—The height andrange-finderNo. 2, Mark II, is acoincidence

range-finderwith an inverted strip type of field of view. It isprovidedwith specialadditionalgearing,andis suitablymountedso as to obtain from the combinedmotions of the coincidencemechanismand the angularelevationof the instrument,a~calemoving in accordancewith the height of the object underobservation,in addition to scalesindicating the range.

The telescopeportion of the instrumentwill be~referredtoas the “range-finder,’’ and the main observerwill be referredto as the “height-taker.’’

The range-finderand its stand are shown diagrammaticallyin Fig. 8, whilst PlatesI and II give views of the instrumenttakenfrom oppositesides. Plate III gives the instrumentwiththe interior partsdismantled.

The instrument is operatedby threeobserversas follows:—

(i) The height-takerlooks into the eyepiece(8) at thecentreof the instrument,and operatesthe workinghead (i~) and the elevatinghandwheel(23).

(2) Thelayerfor line looks into the view-findereyepiece(20)

andoperatesthe traversinghandwheel(24), layingtheinstrumentfor line.

(~)The third observeris the scalereader. He faces theheight-takeron the opposite side of the instrumentand readsthe height, andalso the rangeandangleofsight indicatedon the variousscaleswhen coincidencehas beenobtainedby the height-taker,if requiredtodo so.

45. Although in some casesahard-and-fastdivision cannotbe drawnbetweenthem, it is convenientto considerthe externaland internalcomponentsof therange-finderseparately.

EXTERNAL ARRANGEMENTS

46. The principal external parts are detailed with figuredreferencesin Fig. 8. They canalso be seen in PlatesI, II andIII, in which further componentswhich could not be shownin Fig. 8, will alsobe found. The main componentsarebrieflyconsideredbelow.

15

Outer Tube (i), Fig. 8.47. This is of brassandservesasacoverandsupportfor the

majority of thecomponents:it is paintedservicecolour externallyexcept for a vertical white line which marks the centreof theinstrument. About nine inches from the centre it carries abearing on either side. At - each end are brass end tubes ofslightly larger diameterwhich carry the endwindows (35) andray-shades(3), the latter being closed with leather caps (36)when the instrumentis not in use. The endwindowsadmit thebeamsof light from the objectunderobservationandprotect thepentagonalprismsfrom weatheror accidentaldamage. A canvassun protector(2) is provided for the outertubeto minimize theeffect of the sun‘s rays. The tube is closedwith gunmetalendcaps(5),which screwinto seatingsat theendsof the tube. Fouropensights,oneof which is shown at (~),areprovided; onefortheheight-taker,one4or the layerfor line, andone neareachofthe end windows. They are for rough laying, to enable theinstrumentto bebroughtto bearquickly on the targetin thefirstinstance.HeightScaleGear Case(7), Fig. 8.

48. This is situated above the range-findereyepieceandcoversthe externalheightandrangescalesandenclosesthe gear.It is consideredfurther in the descriptionof the height scale -

gear.

Range-finderEyepiece(8), Fig. 8.49. The externalpart of this eyepiececonsistsof a rotatory

brassmount containing two apertures,either of which can besuperimposedon the internal lens systemof the eyepiece(40),Fig. 14 (seep.22) by rotatingthemount. Onewindow containsplane glass, and tile other a system of reducing lenses. Incombinationwith the internal lensesthey give amagnificationof 25 and 15 respectively,andareso marked. This systemgivesthe samefield of view for both magnifications. Tile completeeyepiececan be focussedby a lever (84), Plate III, which movesover a scalegiving a range of 1 5 diopters. The eyepieceissituatedat the centreof the instrument,andis arrangedat rightanglesto the planeof triangulation. It is fitted with a rubbereyeguard(~5)and leathercap(62) PlateII. A revolving ring isalsofitted within theeyepieceon which aremountedgreen,yellowand red moderatingglasses,a fourth aperturebeingclear. Thering is turnedby a squareheadbelowthe eyepiece,on which areengravedinitials correspondingwith tile colours. Tiìe purposeof themoderatingglassesis to giveadditionalcontrastin tile fieldof view in either very bright or in hazyweather. A binocularattachmentwill be fitted to the eyepiecein instrumentsof futuremanufacture. -

RangeScaleWindow (~),Fig. 8.

~o. Above and to the left of the eyepieceis asmall magni-fying lenswindow throughwilich the internalrangescaleis read.16

ENLARGED PLAN OF HEIGW1• SCALE SEAR CASEAS SEEN BY THE SCALE OBSER’/ER.

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C

CoincidenceAdjustingHead (io), Fig. 8.51. This is situatedto the left of andslightly belowthe range

scalewindow, and is coveredby a protecting ring to preventaccidentalalteration. The screwheadis exposedby revolvingthe ring, and is actuatedby the screw-driverprovided; thisrevolves the coincidence prism enabling coincidence to beadjusted(seeChapterIII, p. 29).

Bearing For~s,Left (ii) and Right (17), Fig. 8.

52. Thesesupportthe instrumentandform bearingsin whichit can rotate in elevation. The range-finder,togetherwith thebearingforks, can be detachedfrom the mounting by looseningthe two securingscrews(22) situatedonebelow eachfork. Thebearingsare slightly eccentricin order to balancetile weight ofthe height scale gear and case attachedto the outer tube.Rotationwithin the bearingscantake placethrough93°,givingan adjustmentof the line of sight from the vertical position to3°depression.

ElevatingGear, Figs. 8 and 9.53. The elevatinggear is of the worm andwormwheeltype

and is shown in sectionin Fig. 9. It is actuatedby ahandwheel(23) situated below the left-hand bearing of the mounting.I’he handwheelhas a two-speedclutch operatedby meansof asmall lever (26) associatedwith the handgrip. A fibre pointedfriction screw (126), Plate II, passesthrough the wormwheelbearing,and is clampedby akeepscrew; its point bearson thefriction ring (64), PlateIII.

54. An elevating handle (52), Plate III, andclamp (34) isalsoprovided for making quick rough settings by revolving theinstrument on its slip bearings,the friction of which can beadjustedby meansof the screwsprovided on the left-handfaceof the left bearing.

55. Within the left bearingis a quadrantrack ~ whichdrives a small pinion (67) carried on the outer tube. Thispinion is connectedthroughacoupling (66) to the specialheightscalegear,andintroducesthemotion dueto theangularelevationof the instrument. An angle of sight scale(57) andan index(~8),Plate II, are provided at the right-hand bearing. Thescaleis graduatedin degreesfrom 3°depressionto 90°elevation.

56. The worm of the elevatinggearcan be adjustedfor wearby a screw(12) and lock nut (seeAppendixII).

TraversingGear. Figs. 8 and 10.

57. The traversinggear is also of tlie worm and wormwheeltype, and is shownin section in Fig. 10. It is actuatedby ahandsvheel(24) situatedon the rotatinghead(103), Fig. 12, ofthemounting, to theright of theheight-taker. This handwheelhasa two-speeddeviceof similarpatternto that of the elevatinghanciwbeel.

17

58. The latestpatternfriction devicefor the two-speedclutchof the elevating and traversinghandwheelsis shown in thefigure. Other types will alsobe found in the Service,but thesewill be modified to that shown as tile instruments passthroughWoolwichfor repair.

59. An azimuthscale(21), Fig. 8, graduatedto give bearingsin degreesfrom o°to 360°,and an index, are provided on tilerotating headof the mounting. The scale may be orientedrelatively to the mounting. The wormwheel is mountedonslip bearingsenablinga quick rough setting in azimuth to bemadeby hand,whilst a fine setting canbe obtainedby meansofthe handwheel. Tile friction of the slipbearingmaybe adjustedby screwsbeneaththe azimuthscaleplate, in which an apertureis cut to give accessto the screws.

6o. The worm maybe adjustedfor wearby meansof a screw

(5~)and lock nut (seeAppendix II).LampSockets(13), Fig 8, and (6i), Plate II.

6i. Theseareprovidedto takethe lampsfor the illuminationof the variousscales. The illuminating gearis further discussedin the descriptionof the standandmounting.

Halving AdjustingHead(15), Fig. 8.62. Covered with a revolving bridge piece to prevent

accidentalalteration, this headis situatedto the right of theeyepiece. By rotating the head, the halving glass can be setat an inclination to the opticalaxis of the right-handtelescope,thus enabling the adjustmentfor halving to be carried out(seep. 29).

AstigmatiserLever (i8), Fig. 8.- 63. This is situatedon the eyepieceside of the instrument,

immediately to the right of the right bearing. - By its meanstheastigmatiserlenses(50), Fig. 14, aresimultaneously thrown intoor out of action. The levermovesoverascalemarkedwith the‘‘IN’’ and “OUT’’ positions.

TVorking Head (19), Fig. 8.64. This is a roller with a milled surface, horizontally

mounted,and lying to the right of the right bearingfork. It isconnectedthroughuniversaljointedcouplingto the jockeywheelof the height scalegear,and thus- communicatesamovementtothe latter, which is a function of the height. Below the headis ahand rest (90), Plate III, giving a supportfor the height-taker’srigilt handwith which lie operatesthe head.

View-finder(20), Fig. 8, and (6o), PlateII.6~.This is of telescopicpatternand is providedfor the use

of the layerfor line controlling the traversingof the instrumentin azimuth. The eyepiece(zo) projectsfrom the outer tubeatright anglesto the line of sight, and is situatedaboutmidway

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betweenthe centreof the instrumentandthe right-Iland end; itis fitted with a rubbereyeguard(s), PlateIII. The objectglassis seenat (6o). The latter can be adjustedboth vertically andhorizontallyafter looseningthe clampingscrew,andthe line ofsight of the view-findercan thus be broughtparallel to that ofthe instrument. After adjustmentthe screwmustbe tightenedup. Fig. ii givesa schematicdiagramof the view-finder.

It consists of an eyepiece (ii~) (ii6), a diaphragm (117)having a circle engravedupon it (wilich can be illuminated fornight work), a roof prism (ii8), andan achromaticobjectglass(119). The eyepiececan be focussed by means of a knurledhead,and the telescopehas a field of view of 6°anda magni-fication of approximately6. A binocular attachmentwill befitted to instruments of future manufacture.

Screws(38), Fig. 8.66. The screwsholding the long and short frames to the

outertubeentertheir seatingsfrom the exteriorof theoutertube,someof them having their headscoveredby external fittings.Eight screwssecurethe short frame, oneof thesebeingshownat(38). The longframeis heldby two screwsonly (74), PlateIII.Tilese haveroundedendswhich fit into suitablerecessestowardsoneend of the frame and on oppositesidesof it. Towardstheotherendof the frame,andattachedto it, is athree-pointsupportbetweenthe frameand theoutertube. A spring plungerat oneof the points of supportholds the frame firmly in its positionwithin the outer tube.

The Stand,MountingandIlluminating Gear, Fig. 8.- 67. The instrumentis mountedon astrongrigid steeltripodstand (28). Tile tripod llead (25) is rigidly attached to thestand andcarriesa rotating head (103), Fig. i~; both of theseare of aluminium alloy. The rotating headis supportedon agimbal bearingwhich can be adjustedby four vertical screws(27) until it is level. Correspondingmarks (53), Plate I, onthe tripod headand rotating headindicatethe position in ~vliichlevelling should be carriedout. The screwsprojectdownwardsbeneath the tripod head,and a spirit level of T type (i6) isprovided upon the rotating head,which enableslevelling to becarried out to within a few minutes of angle. The levellinggearis shown in sectionin Fig. 12.

68. The range-finderand its adjunctsmaybe detaciiedfromthe mountingby looseningthe two securingscrews(22) situatedonebelow each bearingfork. In future manufacturetile conebearingsconnectingthe instrument to the mountingwill formpart of the trunnionson the instrument,insteadof beingpart ofthestandas hitherto. Instrumentswill, in addition,berepairedto this design,which is also silown in the figure.

69. A crosspiece at the baseof the tripod (not fitted on oldermountings) forms a support for the box, battery, switch and

19

resistancecoil (37), Fig. 8, which holds the cells andaccessoriesfor the lighting circuit which illuminates the various scales,levelling bubblesand the diaphragmof the view-finder. Thelampholdersaremadeto takethe bulb 4-volt “G,” the currentbeing supplied from cells, electric, inert “0.’’ Six cells arecarried, three being spares. The remaining accessoriesare,flexible leadswith threeplugs,six bulbs,4-volt “G” in a tray,andthe switchand resistancecoil. Clips are providedon bothstandandinstrument for supportingthe leads.

THE - HEIGHT SCALE GEAR

70. The gear is a mechanicaldevice providing the solutionof the height-findingequation

h r sin aor

Log h = Log r + Log sin abriefly discussedin ChapterI.

71. If, in adifferentialgear,the uppermemberis rotatedinaccordancewith a logarithmic sine scale of angles of sight,and the lower memberin accordancewith a logarithmicscaleofranges, the jockey wheel will revolve round the axis of thedifferential with a motion proportional to a logarithmic scaleof heights.

72. The conversion of the reciprocalrange scalemotion ofthe deflecting prism gear into logarithmic range scalemotion,and of the angularmotion of the range-finderin elevationintomotion correspondingto a logarithmic scaleof sines, is done ineach caseby meansof specially designedtoothed spiral gears.Owing to the natureof the scalesit is not possibleto constructgearswhich will give correct readingsoutside certain limits.The height scale will only give correct indications when theangle of sight to the target lies between10° and70°. For asimilar reasonthe external range scale graduationsare onlycontinuedup to 12,500 yards, rangesabove this limit up toinfinity being read from the internal scale attached to thedeflectingprism, andseenthrough the magnifyingwindow nearthe eyepieceon the outer tube.

73. In the presentdesign the working headis arrangedtodrive the jockey wheel connectedto the height scaledirectly,the range scale and the deflecting prism beifig actuatedindirectly through the gearing. Tile advantageof this arrange-ment lies in tile fact that in the case of aircraft flying at aconstantheight, the images in the field of view, when onceset, can be kept in coincidence by simply elevating theinstrument so as to keep the target in the centreof the field,without rotating the working head. The movement of theinstrumentin elevationautomaticallycontrolsthe positionof thedeflectingprism, whilst the height scaleremainsunalteredsolong as the working headis notturned. When the -target rises

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or falls the imageswill move out of coincidence,andmust bebroughtbackinto alignmentby rotating the working head,thusalteringthereadingof theheightscaleby theappropriateamount.

74. A diagrammaticsectional elevation of the height scalegearasseenfrom the scalereader’sside of the instrumentwhenthe latter is directedvertically, is given in Fig. 13, to which thefollowing indexnumbersrefer. Mostof tile members•aremountedon ball bearings,which, for simplicity, are omitted in thediagram. -

75. Those memberswhich deal with range,angle of sightandheight, are, as far as possible, differentiated in the figureby variations in, shading. Plate IV gives a perspectiveview.

76. The working headoperatesthe jockey wheel (~8)of adifferential through the coupling (i) andbevel gearing(4) and(‘~).

77. The uppermember(~)of thedifferential is controlledbythe rotation of the instrument in elevation by meansof thequadrantandpinion gearalreadydescribed,acting through thecoupling (13), the bevelgears(8) and (9), andthe toothedspiralgears (5) and (6). Tile lattergearsconvertthe angularmotioninto motion in accordancewitil Log Sin a~The lower member(16) of the differential is connectedthroughthe spiral gears(17) and(rg) andthespurgears(so) and (II), tothe deflectingprism gearcoupling (12). The spiral gears (17)and (~)are so designed that while the gear (19) rotates inaccordancewith the reciprocal rangescaleof the range-finder,the gear (17) rotates in accordancewith a logaritilmic scaleofranges.

78. The rangescale(,~)is connectedto the lowermember(~6)of the differential, and the heigilt scale (2) is connectedto thebevel wheel (14) carrying the jockey (r8).

79. In orderto guardagainstdamageto thegearingby forcingit beyondstops,the bevelwheel (r4) is mountedupona frictionslip bearing(r5), which allows it to slip whenthe gearis againstthe stopat eitherend of the travel.

8o. Thewholegeai-is mountedon theoutertubeandprotectedby a case,an enlargedview of which is given in Fig. 8. Thecircular range scale is viewed through a window (31) in theheight scalegearcase (v). The height scale is engravedon asecondcircularscaleconcentricwith therangescaleandis viewedthrough a secondwindow (32). Movable indices are providedfor both scalesby meansof which proportional correctionsinballistic heightandrangefrom 5 per cent, to + 20 per cent.maybe takenup. The indicesare bothadjustedby meansof aknurledhead(r4) (~~)on the gearcase. A small lever(6) is alsoprovided on the latter, by meansof which either tile rangeorheight scale window may be closed by a shutter to avoidmistakesin reading.

8~.Both tile deflectingprism and the height scale- gearareactuatedby theworking hçad(~g)situatedon thewindow sideof

21

the outer tube immediately to the right of the right bearing

fork (ii).

82. The extremerangeson theexternalrangescaleare2,000and12,500 yards. It is graduatedas follows :—

Fromz,oooyds. to 5,000 yds. every100 yds.5,000yds. to 12,500yds. every500 yds.

83. The extremeheightson the height scaleare I ,ooo and30,000feet. It is graduatedas follows:—

From 1,000ft. to 5,000 ft. every 100 ft.5,000 ft. to 20,000ft. every 500 ft.

20,000ft. to 30,000ft. every 1,000 ft.

INTERNAL ARRANGEMENTS

84. The principal internal componentsare shown diagram-matically in Fig. 14, which is not to scale. They are furtherillustratedin PlateIII, whichshowsthe instrumentdismantled.As before, many parts are self-explanatoryandhavenot beenconsideredin detail, but the more important onesare brieflyconsidered below. Numbered references and nomenclaturesare given on bothplate andfigure.

CentrePrism Combination;(41) Fig. 14.

85. This consistsof two main portions,an upperanda lowerprism,which areshownseparatedin Fig. 15. -

86. Theupperprism is aright-angledprism with tile entrancefacenormalto the incidentbeam. The hypotenuseis shapedasa90° roof. The third face is inclined at 45°,andhasanarrowstrip of silvering centrallyacross it. A triangularglassprismis balsame~on to this face so as to protect tile silvering fromdeteriorationand to prevent the reflection of any light whichdoes not strike the silver strip, such light passingon into thetriangularprism without beingreflectedinto the eyepiece. Theincident beamentersthe upper prism by meansof a rhomboidprism, in which it is twice reflected. This is also balsamedtothe upperprism,andis shownin the figure.

87. After enteringtheupperprism theraysarereflectedat theroof andpasson to tue surfacecontainingthe silver strip. Thoseencountering the strip are again reflected and emerge in anupward direction into tue eyepiece. The remainderare notrequiredandpasson into the triangularprism,andarcscatteredby its groundsurfaces.

88. Tile lower prismis aright-angledprism with the entrancefacenormal to the incident beam. The hypotenuseis fiat, andthe beamis heretotally internally reflectedon to the third face;which is inclined at 45°. Tue beamis herereflecteda secondtime andemergesin an upwarddirection.

89. The lower prism fits accuratelyagainstthe under sideofthe upperprism andis balsamedto it. Thus,the raysemerging

22

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LEFT OB3tCT ~ILA5S.

FRONT ELEVATION.

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from the lower prism immediately enterthe upper prism andpassthrough the face on which is tile silver strip, leaving theupperprism parallelto thoseraysreflectedat thesilvering.

90. Two systemsof rays thus finally leave the upper prismparallel to each other and enterthe eyepiece. Firstly, thosefrom the second reflecting surface of the lower prism, andsecondly,thoseproceedingfrom reflection at the silveredstrip.The latter lie asacentralbandacrossthe field of theformerandproducethe appearanceof a strip showing an inverted partialimagesurroundedby acircular erectfield.

91. The whole combination is held in a mount which issecuredto the long frame. -

Halving Glass (42) Fig. 14.

92. This consistsof aplateof parallel-sidedglasswhich canbe set at varying anglesto the optical axis of the right-handtelescopeby rotating the halving adjustmenthead. The move-ment of this memberresults in the raising or lowering of theimagein thestrip field in relationto the imagein themain field,and so enablesthe instrument to be set in adjustment for“halving “ (seep.28).

Internal RangeScala (43), Fig. 14.

93. This is a reciprocalscaleof rangescut on anickel silverstrip attachedto the deflecting prism mount with which itmovesto andfro longitudinally. It is movedby a rack drivenfrom a pinion which is actuatedthrough the height scalegear.It is readagainsta pointer through therangescalewindow (p),Fig. 8. It is graduatedfrom 2,00.0 yards to 25,000 yards asfollows

From 2,000yds. to 5,000yds. every 50yds.5,000yds. to 7,000yds. every iooyds.7,000yds. to 15,000yds. every 500yds. -

15,000yds. to 25,000,)kls.every~,oooyds.Beyond the 25,000yardsgraduationis an “infinity” graduationmarkedby a star,with numbereddivisions to right and left ofit marked + and — respectively,as in Fig. i6.

Fig. 16.

23

Thesegraduationsare used for testing and adjustingpurposes(seeChapterIII). Whencoincidencehasbeencorrectlyobtainedon an infinitely distant natural object, such as the moon or astar, the infinity mark should be opposite tile pointer. Eachnumbereddivision on eithersideof the infinity markis equivalentto 40 yardsat 2,000 yards.

DeflectingPrism (44), Fig. 14.

94. This consistsof a prism of small angle which moveslongitudinally in the left-hand telescopebetween the centreprism combination‘and the coincidenceprism. It is attachedto a mount, which also carries tile internal range scaleand arack. By meansof a pinion actuatedthrough the height scalegear,longitudinalmovementis given to the rack andcommuni-catedto the scaleandprism.

CoincidencePrism ~ Fig. 14.95. This is a prism set in a rotatorymount actuatedby the

coincidenceadjustmentheadthrough a worm and wormwheei.It is capableof rotationaboutan axiscoincidentwith theopticalaxis of the left-handtelescope. The result of this motion is tomovethe imagein themain field to the right or left in relationto the imagein the strip field, so enablingthe instrument to beset in adjustmentfor “coincidence’’ (seep.29).

Object Glasses(46), Fig. 14.

96. Two achromaticobject glasses,one in each side of theinstrument,receive the beamsof light after reflection from theirrespectivepentagonalprisms. -

Frames; Long (48) and Short(49), Fig. 14.

97. The two framesare separatelysupportedfrom the outertube; this arrangementavoidsthe errors due to alteration inbalance of the frame as the deflecting-prism is moved longi-tudinally. The longframe(48) carriesthefixed opticalmembers—the object glasses,the centreprism combination—andalsothe astigmatiserlenses; whilst the short frame (~~)carriesthemoving members—thedeflecting prism and range scale, thehalving glassand the coincidenceprism. The long frame is ofsteel tube, square in section, with cut away portions. Tworectangularframesencircle it towardseither end. The first ofthesecarries two recesseson opposite faces, one circular (73),PlateIII and theother longitudinal,into which theround-endedsupportingscrewsenter: from the secondemergethree studswhich form a support betweenthe frame and time outertube;one of tile studs is fitted with a springplunger,which servestohold the frametightly in position. The frame is thussupportedin a kind of gimbal bearing,and slight distortion of the outertube will not be communicatedto it. The astigmatiserlensesare thrown into the “IN’’ or “OUT’’ position by two rods

24 -

(69) (70), and a link (72), Plate III, carriedon this frame andactuatedby the externallever (x8), Fig. 8; the lensesare heldfixed in either position by springs (71), Plate III. The shortframe is of brassandgun-metal,and is directly securedto theouter tubeby eight screws.

AsligmaliserLenses(50), Fig. 14.

- 98. One of thesefor eachtelescopeis fitted immediately infront of each objective, betweenthe latter and its respectivepentagonalprism. They arecylindrical lensesandaremountedin hingedmountsaboutwhich theypivot, being thrown into theoptical system or withdrawn from it at will, by mechanismwhich hasalreadybeenexplained. Their purposeis to distortpoint objects into streaksor lines, thus enablingrangesto betakenuponapoint of light or otherminuteobjectupon which itwould be impossibleotherwiseto obtain coincidence. As theyare placedoutside the objective of eachtelescopethey do notalterthe focusof thefield of view whentheyare thrown into the“IN” position.

PentagonalPrisms(5k), Fig. 14 andPrismMounts(68), PlateIII.99. At eachendof therange-finderis apentagonalprism,the

left-hand one of which is shown in Fig. r~in section in theplane of triangulation, and in perspective. The prisms arefixed in mounts of castgunmetal (68), Plate III, having pro-jectionswhich fit accuratelyinto groovesin the endpiecesof theoutertube. The depth to which the mountsslide into the tubecan be adjustedby screwson the mounts which act as stops.The prismsareattachedto holders,which are in turn securedinthe mountby threepairsof clampingscrews,eachpair clampinga lug on the holder. By means of thesethe prisms can beadjustedwith referenceto the mounts. When the end capsarescrewed home they pressfirmly against the mounts and hold -

them securelyin position in the outertube.

Fig. 17.

100. The two sides BC, DE of eachprism are silveredandinclined to one another at 450W The silvered surfaces areprotectedby a hard backing, and the upper and lower facesby a thin layerof cork which is cementedto them.

25

rot. Raysof light enteringthe face AB, will, providedthatthey are in the sameplaneas the section,emergefrom the faceAE at right-anglesto their line of entry, after suffering twointernal reflections at the silvered faces. This means that arotationof the prism aboutan axisperpendicularto the planeofthe paper does not affect the angle through which the ray isreflected; consequently,any slight bendingof the outertubeinthat plane will not affect the measurementof the range. Arotation of the prisms about an axis parallel to XY, however,will raiseor lower the imagesin the field of view. Consequently,anybendingof theouter tubeout of the planeof triangulationwill cause-anerror in halving (seep. 28).

The Lath, Adjusting,No. 2 Height and Range-finder,Mark I.

102. The lath,adjusting,is usedalternativelyto an infinitelydistantnaturalobject, for testing andadjustingthe instrumentfor coincidence. -

103. It consistsof abuilt up frameworkof aluminium alloy(121), and is fitted with a small mirror (122), pivot (120) andbubble (123), as in Fig. x8.

104. The mirror is mountedin the centreof the main frame(121),andis protectedby a hingedcover. Thepivot is attachedto the underside of the frame, and is madeto fit in any of thestandsA.A. instruments,or the stand,tripod, of theapparatus,predicting fuze and travel correction (Brocq). The bubble isabubble,spirit, glass“L,” andis fitted in ametalcasemountedon the lower barof theframe; it enablestheframeto be levelledwhenmountedon a stand.

105. Neareachendof the frame is a slight recessin which averticalwhite baseline (125) is painted,on which theheightandrange-findercan be laid. Tile distance between the centresof the two white baselines is exactly equal to the baseof theinstrument,i.e., 2 metres (78.74 inches): both lines are ofexactlysimilar breadththroughouttheir length,

~o6. Instructionsfor the useof the lath aregiven ifl ChapterIII (seep. 31),whilst it is theoreticallydiscussedin AppendixI.

• THE CASE -

107. For transport the instrument is removed frc~mitsmountingandhousedin a woodencase. This is of white wood,the exterior of which is painted service colour. It is metalshodat the cornersandcarries two handles,oneat either end.It is fastenedby four metalclips andfitted with lock andkey.Internalfittings arearrangedto hold firmly both the instrumentand the lath, adjusting, the latter being clipped into the lid.Spare-parts,asdetailedin the table of instrumentdata, arealsocarriedwithin the case.

26

CARE AND PRESERVATION OF THE RANGE-FINDERAND ADJUNCTS

~o8. The instrument and mounting should be frequentlycleanedby aresponsibleman,whomustbe warnedon no accountto removethe glassesfor cleaningpurposes.

109. The cloths provided for cleaning the external glasssurfacesmust be used for no other purpose,and must be keptthoroughlycleanandfree from oil andgrit.

110. The leatherprovidedfor cleaningexternalpartsof theinstrument must not be used for cleaning the glass. Metalpartsshouldbe wipedwith aslightly oily rag.

III. Whennot in usefor any lengthof time the instrumentshould be storedin its case. The interior of the casemust bekept dry, and neither the instrument nor cloths nor leathersshouldbe put into the box unlessthey are quite dry.

112. In wet or dustyweatherthe waterproofcovershouldbeplaced over the instrumentand mounting.

113. Greatcaremustbe takenthat oil andgrit arenotallowedto lodge in the windows: grit is bestremovedby a soft brush.

114. All screwsshould be tightenedup whenevertheyworkloose,andany missingonesreplaced.

ii~. Leatherwork shouldbe slightly oiled from timeto time.

ii6. The lath, adjusting, needsspecialcare in handling to

avoid any bendingof the lath, or erasureof thewhite lines,

27

CHAPTER III

TESTING AND ADJUSTINGINTRODUCTORY NOTE

117. In the preceding chaptersit has been assumedtilatwhen the two partial images of an object have beenbroughtinto coincidencein the field of view, the imagein thestrip fieldappearsto be an exact inversionof the imagein the main fieldimmediately below it, and that the readings then indicatedon the variousscalesarethe true rangeandheightof the object,i.e., that the instrument is correctly adjustedfor ‘‘halving’’and “coincidence” respectively.

~ Thie instrument,however, may be out of adjustmentin one or both of theserespects. It must, in consequence,befrequently tested,and readjustedif found to be at fault.

119. The adjustingheads(~5)and(to), Fig. 8, by meansofwhich theseerrorsin halving and coincidencecan be correctedhave been already described. Tile adjustmentsdo not takemany minutes to perform andpresentno difficulty; but thecoincidenceadjustmentshould be carried out with both careand deliberation, and, asfar aspossible,only underfavourableconditions.

120. To obtain the greatestpossibleaccuracyin testingandadjusting the intrument, the high power magnification shouldinvariably be used,and the instrumentshould be testedandadjustedby the individual who is about to use it.

HALVING ADJUSTMENT

121. When the instrumentis out of adjustmentfor halving,the imagein the strip field may appeareither too high, as inFig. 19, or too low, as in Fig. 21.

Whenhalving is correct, tile lower separatingline shouldcutthe samepart of the objectin both fields, as in Fig. 20.

Fig. 19. Fig. 20. Pig. 21.

28

122, A smallhalvingerror will not produceanyeffect on thecoincidence setting in the caseof an object withi parallelsidesat right-anglesto theseparatingline; but thecoincidencesettingwill be seriouslyaffectedby evenasmallerror in halvingif thelines of the objectupon which observationis madeare inclinedto the separatingline. It is thus advisablealways to test thehalving before commencingany observations. It is essentialthat the eyepieceshould be carefully focussed,and all adjust-mentscarriedout, by the observeraboutto usethe instrument.

123. To test the halvingadjustment.

(i) Select any well-defined object and bring the imagesinto approximate coincidence in the field of view.

(2) Direct the instrument in elevation so that the partialimagesdo not crossthe separatingline. -

(3) By meansof the elevatinghandwheelrotate the instru-ment so as to causethe- two images to approachthe separatingline.

(~)If halving is correct, the two imagesof a point on theobjectwill meeton the separatingline, as in Fig. 20. If thelower imagetouchesthe line first, the strip image is too high,as in Fig. ~ and if thestrip imagetouchesthe line first, it istoo low, as in Fig. 21. In either of thesecases the halvingrequiresadjustment.

124. To correct a halvingerror.(i) Rotatethe halving adjustingheadcover until the head

(r5), Fig. 8, is exposed. Rotate the head until the error iseliminated.

(2) Check the adjustmentby repeatingthe halving test.(~)Rotatethe coverback into the closedposition.

COINCIDENCE ADJUSTNENT

125. It is important that halving should be tested,and, ifnecessary,adjustedwith specialcare,beforeproceedingto adjustcoincidence,as a small error in the former may causean errorin the latter.

The coincidenceadjustmentmay be tested:—(a) On an objectat aknown range.(b) On an infinitely distantobject (naturalinfinity).(c) By means of the lath, adjusting (artificial infinity).

The aboveareplacedin orderof merit.Tests (a) and (c) are further consideredin later paragraphs

dealingwith the correction of a coincidence error. Test (b) isgiven in detail immediatelybelow: the first two paragraphsofthis test are commonto all three methodsof testing, and thethird paragraphis commonto methods(b) and (c). In methods(b) and (c) readingsmustbe takenin divisionsaboveandbelowthe infinity star,noting them as + and — respectively.

29

126. To test the coincidenceadjustment. - -

(i) Ensure that halving is correct by testing as alreadydirected,andadjustingif necessary.

(2) Direct the instrumentupon the object. If the moon isusedthe verticaledgeshould be selected. If astar, the astig-matiser lensesshould be used, and care taken that the samestar is observedin both fields.

The instrumentshould never be directed upon the suj (whichis thus not available as a natural infinity), even with i/ic aid ofcoloured glasses,as rays come to a focus within the instrument,and damage might be causedboth to the instrument and to timeobserver’s eyesight.

(~)Take a series of at least ten observations,reading thescaleat eachsetting thus:

Beforeadjustment Afteradjustment—2’2 +0~3

+0’2- —20 +0’2

—1’8 +0~2—2~0 —0’2—1’6 0’O—1~5 —0~1—1~5 4-0.2—1~4 —0~2

+01

—17’3 +0’7

Mean... —1~73 Mean... +007

Add the readings(taking accountof the+ and —) anddivideby the numberof readings. If the resultantmean is zero, ordoesnot exceed f O~I3divisions, the instrument is in correctadjustment. If theselimits areexceededthe coincidencemustbeadjusted. The first set of readings indicates that adjustmentis necessary. The secondset, taken after adjustmenthas beencarriedout, indicatesthat this hasbeendonein a satisfactorymanner. (Eachnumbereddivision on the scaleon either sideof the infinity star is equivalentto 40 yards at 2,000 yards.)On no account should the coincidenceadjustmentbe alteredunlessthe needfor adjustmentis definitely establishedby theabove test.

127. To correcta coincidenceerror.

This maybe done:—

(a) On an objectat aknownrange.(b) On an infinitely distantobject (naturalinfinity).(c) By meansof the lath, adjusting(artificial infinity),

There is no fundamentaldifference of principle between thethreemethods,but theyareplacedin their relativeorderof merit.

30

128. (a) On an object at a known range.

The t~strange should be accuratelyknown and should bedeterminedby survey methods.

A well-definedobject, such as a flagstaff, tower,or chimneywith asky background,is themostsuitableobject. The rangeis comparativelyimmaterial,so long as it exceeds2,000 yards;the essentialconditionsare that the range must be accuratelyknown, and that the definition and visibility must be good.

(i) Takea seriesof ten observationsof tile rangeand findthe mean. -If the difference between this and thetruerangeiswithlin thepermissibleerror* (seeAppendixI) the adjustmentis correctandshouldnot be altered.

(2) If the difference exceedsthe permissibleerror, adjust-ment is necessary.

Setthe truerangeon the internalrangescale,andbymeans of the coincidenceadjusting head bring theimages into coincidence,taking care not to disturbthe working head.

(3) Takea new seriesof ten readingsand find themean’asbefore. If the difference betweenthis and the truerange is within the permissibleerror the instrumentis now in adjustment; if not, it must be readjusteduntil this is so.

129. (b) On an infinitely distant object.(i) Rotate the working headuntil the internal rangescale

reads infinity.(2) Expose the coincidenceadjusting head (ro), Fig. 8,

by rotating its cover plate. - Rotate the head bymeansof the screw-driverprovided,until the partialimagesare in exactalignment.

• (~)Takeanew seriesof ten readingsand find the meanasbefore. If now correct to within ± o~I3divisionsthe instrument is in correctadjustment,but if not,

• the proceduremust be repeateduntil it is so.(~)Rotate the cover plate into the closedposition.

130. (c) By meansof the La/h, Adjusting.(r) Place the lath on its stand,andset it up at least 200

yards from the height and range-finder with thewhite base marks facing the latter. Set the lathapproximatelyparallelto the instrumentand level it.

(2) Swing down the mirror cover, and standingbehindthelath look into the mirror, moving the headuntil thepupil of the eye is reflectedjust below the upper edgeof themirror. Tilt the lath to front or rearby means

* In the caseof this instrumentapproximatelyequalto thesquareof-the numberof thousandsof yards in the range, e.g., iô yardsat 4,000yards.

31 -

of the stand,until the instrument is just seenabovethe mirror, care being taken not to tilt the lathsideways.

(~)Traversethe lath until the centreof the reflectedpupilis seen to be exactly in line with the centreof theinstrument,asin Fig. 22, and clamp it in thusposition.The centreof the instrumentis markedwith averticalwhite line.

(~)Lay the instrument on the lath and adjust the formeruntil the lower edgeof tue strip field is parallelto thelath and the partial images of the two base markson the lath are visible in the field of view, as in Fig. 23.

(5) Bring thepartial imagesinto exactcoincidenceby meansof the working head, as in Fig. 23a, and note the readingabove or below the infinity mark, as the case may be.Find the mean of ten observations taken in this way.Proceed to adjust and retest, as in (b) if the mean is.found to exceed ±O~I3 divisions.

Fig. 23a.

Fig. 22.

Fig. 23,32

After carrying out thecoincidenceadjustmentby anymethod,the instrument should be retested for halving and readjustedif found to be at fault. This is necessarybecausea largemove-ment of the coincidenceadjustingheadwill slightly upsetthehalving.

131. In order to enable the layer for line to follow a targetaccuratelyit isnecessaryfor the lines of sight of the range-finderandview-finder to be parallel. -

Instructions for making them so are given below, and oncethey are correctly adjusted it should seldom be found necessaryto alter their alignment.

To adjust time alignmentof the view-finder.

On the front plate containing the object glass (6o), Plate II.of the view-finder are three screw heads with the followingwording engraved against them

(a) Clamp. Unclamp,(b) Raise. Lower.(c) Left. Right.

Lay the range-finder on some distant stationary object andbring the images into coincidence in the centreof the field of view.The imageof the point of the object laid on should thenbe atthe centre of the circle in the view-finder.

If it is not, unclamp screw (a) and turn screws (b) and (c) asTequired until it is so, then reclamp screw (a) ‘taking carethat thealignmentis not thrown out in doing so.

132. In addition to the aboveoptical adjustmentstherearetwo mechanicaladjustmentsthatwill be necessaryfrom time totime.

These are the adjustment of:—(a) The azimuth friction slip bearing,(b) The elevation friction slip bearing.

Theseadjustmentsshouldnot be carriedout moreoften than isabsolutelynecessary,andshouldbe doneby an artificer. If noartificeris availabletheymustonly be madeunderthe personalsupervisionof an officer.

Instructions for these are given below.

To adjusti/me azimuthfriction slip bearing.

133. Loosen the azimuth scale (21), Fig. 12, by unclampingnut (114), Fig. 12, and revolve it until the circular aperture isover the screw-in the rotating head (103), Fig. 12. Remove thescrew and rotate the head until each of the six friction screws is,in turn, exposed through the aperture. Adjust the frictionscrews as required. It is advisable, when performing this

(Hi)

adjustmer~t, to mark the screws so as to ensure an evendistribution of pressure round the friction ring (iiz), Fig. 12.The adjustment should be continued until the ‘rotating headresponds readily to a movement of the traversing handwheel,andat the sametime, when employingquick setting, themove-ment of the range-finderis smoothand uniform. After adjust-ment, replacethe cover screw.

To adjust the elevationfriction slip bearing. - - -

‘34. First tighten the five screws in the left face of the leftbearing of the range-finder, until, when using the quick settinghandle, the range-finder can only be elevated with difficulty.Then loosen each screw an equal amount, until the movement issmooth and uniform.~ •

34

CHAPTER IV

DRILL FOR THE HEIGHT AND RANGE-FINDER- NO. 2, MK. II.

- TypeU.B.2. -

GENERAL DUTIES135. The detachment is composed of three men:— -

...‘ - ... Height-taker.- 2 ... ... Layer for Line.

3 ... ... Reader.The duties of each man are as follows

DUTIES OF I. -

~. He is. in charge of the detachment,and is responsibleforthe correctness of the DRILL.

2. He supervisesall TESTS and ADJUSTMENTSof the instru-ment, and is responsible for its correct SETTING UP, LEVELLINGand ORIENTING. He teststhe ELEVATING GEAR. -

3. In action, he operates the ELEVATING HANDWHEEL, andby means of the WORKING HEAD makes COINCIDENCE. Heorders “READ” whencoincidenceis correct.

DUTIES OP 2.

I. He assistsI in SETTING UP the instrument,and testsandadjuststhe VIEW-FINDER andteststhe TRAVERSINGGEAR.

2. In action, he lays the instrument on the target over theOPEN SIGHTS, andfollows the targetwith the VIEW-FINDER, byoperatingthe TRAVERSING HANDWHEEL. -

DUTIES OF 3.i. He places the STAND in the position indicated by the

B.C. assistant,and, when the instrumenthas been set’ up,ORIENTS it.

2. In action, he reads HEIGHTS or RANGES asordered,closingthe shutter of the scale not required. He calls out his readingto the battery commander.

NOTE.—He will only call out HEIGHTS if time angle of sightis between100 and 700.

3. He is responsible for all lighting circuits. -

136. POSITIONS AT DETACHMENT REAR.The detachment falls in—I on the right, and 3 on the left

in single rank.35

(711) fl 2

137. To TELL OFF.

Section commander.Section—Telloff.’’

i numbers himself i, the next man2, andthe left handman 3.

138. To EXAMINE EQUIPMENT.

Examination of equipment will be carried out before leavingthe gun park. When in action, this procedure should be carriedout at least once in every 24hours,andadvantageshouldbe takenof any interval to examine and test equipment.

Section commander.Section—Examineequipment.’’

i, assisted by 2, removes the instrument from its box, mountsit on the stand, which has been placed in position by 3, andclamps it with the two securing screws.

2 teststhe traversinggear; i teststhe elevatinggear.

If the friction plate of the former, or-the friction ring of thelatter require adjustment, this should be carried out by anartificer. If no artificer is available,the adjustmentmustonlybe carried out under the direct supervision of an officer.

i levels the instrument,which is traversedby 2 until thearrow on the rotating head is opposite the line on the tripod head,operating each pair of screws in turn. After levelling, allscrews should be tight. 2 then traversesthe instrumentthrougha large arc, and I re-checks the level. If the bubbles do notremain central, they should be adjusted by an artificer.

I uncovershis eyepiece,focusses,andselectsashigh amagni-fication as is consistentwith atmosphericconditions. 2 uncoversthe endwindows, and,assistedby i, testsandadjuststhe view-finder for line andelevation.

i sees that the moderating glass ring rotates correctly: hethen carries out the “halving” and “coincidence” tests, aslaid down in Chapter III (seep.28).

3 teststhe lighting circuits.As soon as the examination is completed, the detachment

form “Detachment Rear.’’ -

i reportsto the B.C. assistant“U.B. 2. readyfor action,’’ or

otherwise.139. To Co~iriINTO ACTION. -

Section commander. - -

Section—Action.’’ -‘ - -

3 places the stand on a level platform, and presses it ‘intothe ground by means of the flanges. i, assistedby 2, mountsandlevels the instrument. - - - -

2 and 3 orient the instrument.

36

To Orient:—

2 lays on the point ordered.

3 unclamps the azimuth scale, sets the bearing as orderedand reclamps. ‘ - ‘ -

3 sets B.H. corrector to zero, if no correction is ordered.If time permits, the “halving” and “coincidence’’ tests will

be carried out. - -

The detachment thentakeup theirpositionsin action:~—

r at the range-finder eyepiece.2 at the view-finder.

3 at the range and height scales.

140. TARGET ORDERED BY SECTION COMNANDER.

Battery commander’s assistant.“Target Bearing Angleof Sight . . . .“

3 puts on the bearing and angle of sight ordered, -~and ~look for the target over the open sights.

When 2 seesthe target, he lays first by the open sight then -

by the view-finder,usinghis quick motion handle. As soonasx seesthe target in his field he reports“ON” and follows thetarget by turning the elevating handwheel: 2 folds back thequick motion handle, and follows the target by turning thetraversinghandwheel. The low gearson both handwheelswillbe used whenever possible. 3 will check bearing and angle ofsight when icalls “ON.”

NOTE.—If the target is first seenby a number other than 2,that numberwill assist2 to lay time instrwnenton the target.

2 keepsthe target in the centreof his field, and I makescoincidences continually on the lower “dividing line” in hisfield. -

- After each height has been read, HE MUST ROTATE THEWoRKING HEAD AT LEAST HALF A TURN in either direction,before making a new coincidence.

I orders “READ’’ wheneversatisfiedthat the coincidenceiscorrect: 3 then reads and immediately calls out to thebatterycommander the first height. After this first reading, 3 willonly call out the MEAN of each set of three readings, and thenonly in the intervals betweengroupsof fire.

At “Range Control,” 3 readsand calls out the ral-ige con-tinuously,wheneverI orders “READ.”

If the target is lost, I will report to the B.C. assistant,l~U .B.2. TargetLost.” The target will be picked up again as

soon as possible. -

37

141. CALLING OUT HEIGHTS. -

Heights should be called out as follows, in a voice loudenough to be heard at the control post :—

4,000—” HeightU.B .2.—Fourthousand.” -

6,500—”HeightU.B. 2.—Six,Fivehundred.”-‘ io,ooo—’ ‘Height U.B.2.—Ten thousand~“

12,250—’‘Height U .13.2.—Twelve, two,fifty.“

13,000—’ ‘Height U.B.~.—Thirteenthousand.”

142. CEASE FIRING.

Sectioncommander. -Section—Ceasefiring.’’ -

I replaces cover on ‘his eyepiece, 2 the covers on the endwindows. The canvas cover is placed on the instrument.

143. MOVE OFF. - ‘ - -

Section commander .,. ‘ ‘ - ‘ -

Section—Moveoff.”

2 depresses the instrument on to stops. - ‘ - - ‘ -

i and 2 remove the instrument from its - stand, double withit to the instrument lorry, and replace it in ‘its boX.

3 carries, and replaces on’ the lorry, - the stand and lOosestores. ‘

144. PACK U~(OR REPLACE STORES).

Section commander, - -

Section—Pachup’’ (or “Replace stores’’).i replaces the cover on hIs eyepiece.2 depresses the instrument on to stops, and replaces the

covers on the end windows.i and 2 remove the instrument and replace it, 3 replaces the

stand and loose stores.

38 -

CHAPTER V

NOTES ON THE TRAINING OF HEIGHT-TAKERS

145. The following notes are intended to assist instructors inthe training of men as height-takers from the most elementarystage of individual instruction to efficient team work as adetachment. It is only possible to obtain the highly accurateheight-finding results of which the instrument is capable bymeans of continuous practice in coincidence work, and by theattainment of a very high standard of laying. In order that thesystem of instruction may be similar in each brigade, the brigadecommander should personally supervise it, an officer or qualifiedN.C.O. being detailed to take charge of the instruction of allheight-takers in the brigade. In addition to the authorizedestablishmentof height-takers,an adequateandefficient reserveto replace possible casualties must be maintained. Every A. A.Section should have at least two trainedheight-finderdetach-ments. The courseshouldbe aprogressiveone,beginningwitha few short lectures, which should be devoted to explaining theworking of the instrument, the names of the various parts andtheir uses, and the errors that are commonly made.

146. An explanation in simple terms of the general ‘principleof a coincidence height-finder is given below. The U.B.2.height and range-finder measures the range along the lineof sight, and, as it is layed on the target, it also measuresthe angle of sight. These two measurements, by means of aspecial gearing, are converted into height. The accuracy ofthe range that is automatically found by making a coincidencedepends on the measurement of an extremely small angle. Thisangle is so small that it is unlikely that three consecutive readingswill give identical results.

Assuming the target is at T, Fig. 24, and the range is8,ooo yards, the angle on which the range depends is the angleA T B. In the Figure, A B is the base which, for the U.B.2.is 2 metres, or approximately 8o inches. Employing thegunners rule, which is that

the base iii inchesThe angle subtended in minutes the range in ioo’s of yds.

8o . -

the size of the angle A T B is ~= i’ooo minutes,

For a range of 7,900yards, the size of the angle is

= I’013 minutes. -

7939

0

The variation in these two angles is less than one second ofangle. This extremely small difference can only be detected byvirtue of the magnifying power of the eyepieceof the instru-ment,andeventhen it requiresgreat discriminationof vision.Height-takersmust, therefore,understandthat it is seldompossible to get any coincidencethat is absolutelycorrect,butthat on every occasiona fresh coincidencemust be made,andthat’ the mean’ of three or four readings, all of which may beexpected to be slightly different should give a good mean height.The main principle to be observedby height-takersis, not tomake all efforts to maintain coincidence, but, as soon as asatisfactorycoincidencehasbeenmade and read off, to breakcoincidence and then to re-make it. Accuracy and rapidityare the two main factors that constitute good height-finding;until a man has obtained reasonable proficiency in these twoessentialdetails, it is an absolutewasteof time to attempttotrain him on a moving target.

Firs~Phase. -

In the initial period of training, no times should be taken.Everything should give way to consistency. When the manhas shown, by the consistencyof his readings,that his brainand eye are sufficiently~ trained to appreciate an accuratecoincidence, his work should be checked against the clock. - Thisfirst phase of ‘training mayamount to several weeks. The resultsobtained may show that the man has not the necessary eyesightand judgment required-to permit him ever to become an’efficientheight-taker. . - - -

Fig. 24.

40

SecondPhase.The second phase, which is speed in obtaining results, is

almost equally essential. If a man cannot make up his mindalmost instantaneouslyas to what is an accuratecoincidenceon a stationery target, he will be intensely slow or inaccurateon a moving target. For when heights to a moving target arebeing taken, it is seldom that the laying of the instrument willbe so consistent that a prolonged scrutiny can be maintained on adefinitepresentationof the target for obtaining coincidence, -

Third Phase. - ‘ -

The third phase is the rapid production of the mean ofthree or more height readings. It is intended that all theabove training be carried out on an indoor coincidence teacher.

Fourth Phase.The fourth phase is training on outdoor aerial targets

in order to obtain a very high degree of efficiency in laying.The necessity for extreme precision in laying, is due to thefact that a fast moving target has to be kept on the dividingline, and that the strip field’ is only five minutes in height.If coincidence is attempted on a six-foot strut of a machine, andthe range is 7,200 yards, the whole strut will subtend, to theunaided eye, I minute of angle. As the strut has to appearin the strip and also in the general field, a precision of layingamounting to about half a minute of angle must be maintained.Such extremely accurate laying can only be attained by constantpractice. The height-taker will not give the order to “read”as he will be almost solely concerned with maintaining an accuratelay, and no times need be recorded. The magnification usedduring this phase should at first be the low power (x ~5); whenprogress has been made, the higher power (x 25) should beemployed.

F1~ftimPhase. -

The last phase is training on aerial targets with a view toobtaining accurate heights in quick time. -

In all the training referred to in -phases (2), (~)and (s),careful reCords should be kept’ and recorded on a form of thetype shown below:—

Rank Name Height Mean Error Time Remarks

These records can be kept conveniently in Army Book 136ruled in columns, - . ‘ - -:-‘ 41

APPENDIX I

THEORY’ OF COINCIDENCE RANGE-FINDING- - ‘ HEIGHT-FINDING. -

THE RANGE-FINDING FORMULA

AND

-i-. If 6 be the parallax angle in radians, B the base of therange-finder in yards, and Rthe range in yards as in Fig. 25:—

-~ B ~-

Fig. 25.

‘~•1”-R

B- - - ‘ TanO==~

And since 0 is always very small, as wasthis may be written :—

B

This is the range-finding formula.

shown in Chapter I,

2. ERRORIN RANGE DUE TO AN ERRORIN OBSERVINGTHE PARALLAX ANGLE

Differentiating the above:—

dO BdRR2 . . . . (I)

This indicates that a small increase of parallax angle willcorrespond with a small decrease of range, and vice versa; andthat the magnitude of the change in the angle is B/R2 times thatof the change in the range. - ‘ - -

If a is the small change in the angle which corresponds toa change in range of x yards,since the change may be in eitherdirection :—

or

. ~ . (2)

- Thus, if in measuring the angle of parallax a small error ismade, it is seen that

(i) For any given range and base, the error in range isdirectly proportional to the angular error of observa-tion, but is of oppositesign.

(2) For any given errorof observationandbase,the error inrange is directly proportional to the square of the range.

(~)For any given range and angular error of observation,the error in range is inversely proportional to the base.

The question of magnification has not so far been con-sidered; but, as was shown in ChapterI, accuracyhas-beenassumedto be directly proportionalto the magnification M ofthe instrument. Hence -the ‘error of alignment of the partialimages will be proportionately reduced with an increase ofmagnification, and equation (2) may be further modified toinclude this quantity, and now becomes:—

R2a -

- x=±~—~ (~)which is the basic formula of coincidence range-finding. -

- - PRECISION OF COINCIDENCE RANGE-FINDING -

3. ‘By precisionis meantthe closenessof the observationstothe’ mean observed range, irrespective of whether - theyapproximate in value to the true range or not. The degree ofprecisionis ascertainedby finding the meanerrorof rangein theusual way. The smaller the mean error, the greater the precision.’

4. It has been experimentally determined that the meanerror of alignment, in the case of a normal well-trained observer,under good conditions of observation, for a small series ofobservations, should not exceed ~ x~seconds for the unaidedeye. From the above it will be seen that this will be reducedto 12/M if the eye is aided by an optical system of magnification M.

Putting - a = 12 in equation (~)12

since there are 206,265seconds in a radian.Then

R2x = ±0.0000582 ~

or

X=±58.2 (ii.)

where r is the number of thousands of yards in the range. Thisequation is common to all coincidence range-finders.

For the height and range-finder No. 2, Mark II, with a baseof 2 metres and the higher magnification 25 it becomes - -

- x = 1.064 r2 . (5)This equation gives the mean error of range corresponding to themean error of alignment of the partial images, which should not

43

be exceeded in~ a small series of observationsmadeunder goodconditions by a normal well-trained observer.

5. A table (Table A) of permissiblemean errors—orper-missibleprecisionerrors—calculatedfrom this equationis givenon p. 47. -

As a rough rule it may be stated that, for this instrument,the permissible- mean error of range is equal to the square ofthe number of thousands of yards in the range. -

ACCURACY OF COINCIDENCE RANGE-FINDING

6. Of equal importance with the precision or consistency ofa series is the accuracy of that series. That is, the closenessbetween the mean observed range and the true range. -

7. By careful adjustment of the instrument as detailed inChapter III, any- systematic error can be practically eliminated.

8. The method of adjustment, however, like that of range-taking, - is~ dependent on the alignment of the partial images,and both processes are therefore liable to similar errors.

9. After adjustment for coincidence it is therefore to beexpected that a small error will still remain, which may be less,but should not be more, than the mean error of alignment.

- 10. - Consequently the mean observed range in the case of asmall series of observations should not differ from the unknowntrue range by more than the amount given in Table A, the samerange-takerbeing employedbothfor adjustmentandfor subsequentobservationwith the sameinstrument.

- ii. Table A is therefore not only a criterion of good precision,but also of good accuracy; that is to say, in the case of aninstrument adjusted, and subsequently used, by a goodobserver- (i) The precision, or mean error of range, should not exceed

the figure laid down as permissible.(2) The difference between the mean observed range and the

true range should not exceed the same figure.12. Experiencehas shown that little advantage is gained by

taking more than a limited number of observations on which toadjust the instrument. Owing to the difficulty of taking manyobservations under exactly similar conditions,somethingof theorder of 10 readingsseems to be most suitable. -

13. Under exceptionally good conditions a better performancecan be obtained than that given in Table A, and sometimes itwill be found- to be worse. The table is, however, based onnormal conditions, and, as a rule, the permissible errors shouldnot be exceeded. Themore experienced the observer, the-bettershould be the results.- - ‘, ‘ . -

14. In the case.. of. a ,single - observation with a carefullyadjusted instrument, the-’ accuracy, or difference between theobserved range and true range, cannot be expected to be as good

44

as in the case of the mean of a small series of observations. Themean angular error in the case of a small series being 12 seconds,the probable error of a single observationis 12 x o’8453, or about10 seconds, and the maximum error should not exceed four timesthis, or 40 seconds for the unaided eye. Adding to this the errorof adjustment of 12 seconds, it may be said that the error whichshould not be exceeded in the case of a single observationis 52seconds for the unaided eye, or about 2 seconds if the magni -

fIcation 25 is employed. The permissible error in range is thus~- or about 4~33times that given in Table A.

If x1 denotes the permissible error of a single observation

Xi=4’61 r2 . (6)A table (Table ‘B) of permissible errors for a single observation

is given on p. 47 which is calculated from this equation.15. The probability of a single observation having as large an

error as that given by (6) is very small. It is an even chancethat the error of a single observation will be greater or less than Pwhere :—

p2 I2~+ 102orp ± I5’62

for the unaided eye. Taking this as ~6 seconds, it is an evenchance that the error of a single observation will be greater orless than about ~ = x~times the figures given in .Table A.

16. Only the higher magnification of 25 has so far beenconsidered; if the lower power of 15 is used, -the figures obtainedwith power 25 must be multiplied by ~.

PRECISION -AND ACCURACY OP HEIGHT-FINDING17. Let H and R feet respectively be the height and range to

an object under observation which is assumed to be flying at aconstant height, and let 0 be the angle of sight, as in Fig. 26.

Fig. 26.45

Then - R = H Cosec 0 . (.~‘)-‘ ... dR=dllCosecO (8)

where dH and dR are corresponding very small changes in Hand R.’

dR thuscorrespondswith x in equation (3), and taking theappropriatesign (foran increasein rangecorrespondsto adecreasein parallax angle) :— - -

R2a -

dR=-~Whence - ‘ -

R2a— -~-~= d H Cosec 0. . - from (8)

Substituting from (~) - --

H2 adH=~~-~~-MCosecO , . . (~)

showing,’ provided they are of the same order of magnitude,that the effect of small errors in measuring the angle of sight is

- negligible in comparison with the effect of small errors inobtaining coincidence.

~8. Taking the higher magnification 25, the mean error ofalignment ±12 seconds as before, and calling the resulting errorin height y feet :— ‘ ‘ -

- 12H2

or ~‘ ±206,265 X 25 X 6~56I68CosecO- y = ±O~35h2 Cosec 0 . . . (io)

whereh is the number of thousands of feet in the height, and ythe permissible mean error of height which should not beexceeded in a small series of observations made under goodconditions by a normal well-trained observer.

‘9. It will be noted that a positive error in height is dueto a negative error in measurementof parallax angle.

20. Table C is calculated from equation (10) and showspermissiblemeanerrors in height at various heightsand anglesof sight. It is a table of both accuracyand precision. Thefigures in it must be multiplied by 4~33to obtain the permissibleerror of a single observation; and it is an even chance that the errorof a single observation will be greater or less than about I~timesthe figures in the table. With a magnification 15 these errorsmust be further multiplied by ~-.

21. Furthermore, static targets only have been considered.In the case of a moving target it is more’ difficult to makecoincidence; and to allow for this, the figures in all the tablesmust be multiplied by an empirical factor. This factor remainsto be determined by experiment.

- 46

22. The tables may also be looked upon as showing theuncertainty of observation of ranges and heights at given ranges,heights and angles of sight, respectively.

TABLE A TABLE B

- PermissibleMean Error of Range Permissible Error of a Single(Precision). Observation.

PermissibleError of MeanObservedRange(Accuracy). ‘ - x~=4~6lr~

x=1~064r2x=Error in yards. x1=Error in yards.r= Rangein thousandsof yards. r= Rangein thousandsof yards.

Range x x~

yards yards yards2,000 4 183,000 10 This table is 41 This table is4,000 17 for usewith 74 for usewith5,000 27 Magnification 115 Magnification6,000 38 25. 166 25.7,000 52 To convertfor 226 To convertfor8,000 68 usewith 295 usewith9,000 - 86 Magnification 373 Magnification

10,000 106 15 461 1511,000 129 multiply by 558 multiply by12,000 153 -~ 66413,000 180 78014,000 208 - 90415,000 239 1,03716,000 272 1,18017,000 307 1,33218,000 345 1,49419,000 384 1,66420,000 426 1,84421,000 469 - 2,03322,000 5i5 2,23123,000 563 2,43924,000 613 2,65525,000 665 2,881

47

TABLE C~Uncertainty of Observation (in feet) at Various Heights,

y = 0.35 h2 Cosec 0

Heightfeet

Angle of Sight

10° 20° 300 40° 50° - 60° 70°

1,000 2 1 1 1 — —

2,000 8 4 3 2 2 23,000 18 9 6 5 4 44,000 32 16 11 9 7 65,000 50 25 18 14 11 106,000 73 37 25 19 17 147,000 99 50 34 268,000 65 45 359,000 83 57 44

10,000 102 70 5411,000 123 85 6512,000 147 101 7813,000 172 118 9114,000 137 10615,000 Errors not 158 12216,000 given where 179 13817,000 range would 202 15618,000 C X C e C d 227 17619,000 12,500yards. 253 19520,000 21821,000 y’=Errors in feet. 23822,000 h=Height in thou- 26323,000 sands of feet. 28824,000 e=Angle of sight. 31325,00026,000 This table - is for use with27,000 Magnification 25. To convert28,000 for use with Magnification29,000 15 multiply by 4~.30,000 -

2229374656667790

103117133148165183202221242263286309334358385

202633404958687991

103116130145162178194214233253273295317340364

369

1318 -

2430

- 37455463738495

108121134149164180197214233252271292313335

48

THEORYOF THE LATH, ADJUSTING

23. Consider two vertical rods T and T’, Fig. 27, at adistance b apart and at a range R’ from the height and range-finder X Y, the line T T’ being parallel to the base X Y of therange-finder. Let the length of the latter be B and the angleX Y Z a right-angle.

x’

Fig. 27.

z

T

T’ T

Fig. 28.

(~Th24. If coincidence be made between T in the main field and

T- in the strip field, as in Fig. 28, the range recorded by aninstrument in correct adjustment will be R’.

25. If coincidence be made between T in the main fieldand T’ in the strip field, as in Fig. 29, the range recorded will beR, just as if coincidence had been made on a single rod at Z.

49

I

t

-4--------—--13 ——----—---~-

\~IT~T’

Fig. 29.

(711) C

26. Owing to the optical construction of the instrument,the movement of the images in the main field to the leftcorresponds to an increase of range, and vice versa. The lowestrangethat can be measuredis 2,000 yards.

From similar triangles in Fig. 27,

R_R-R’ -

- B bor

BR’R B—b

Thus when b = 0, the range recorded is R’b = B, the range recorded is ~

27. Consequently,if the rodsT andT’ be placedatadistanceapart equal to the base B of the range-finder, and the partialimages of T in the main field be brought into coincidence withthat of T’ in the strip field, the range recorded on the internalrangescalewill be infinity, if the instrument is in adjustment.

28. In practice the rods are replaced by the lath, adjusting,on which are painted two white lines whose centres are exactly2 metresapart, i.e., a distance equal to base of the instrument.It is essential that these lines should be of exactly the samebreadth, so that their right and left edges can be brought intocoincidence simultaneously.

29. When adjusting the range-finderon the lath, greatcaremust be taken to avoid the errors inherent in its use. Theseare :—

(a) Want of parallelism between instrument and lath.

(b) Lath incorrect in length owing to damage or warping.(i) The following errors in range will occur if, when

adjusting the instrument, the lath is inclined at an angle y tothe range-finder, the lath being set up 250 yardsfrom the latter.

RangemeasuredR = 5,000 10,000 15,000 25,000

Errors fory=1° 15 6o 135 375

2° 6~ 244 549 1525

30 137 548 1233 3425

The meansprovided for obtaining parallelism between lathand range-finder are such that the error should be less than 10.if the lath he placed at twice the above distance away, the errorswill be halved. Consequently the lath should be placed as faraway as possible from the range-finder, provided that the whitemarks on it can be clearly seen in both parts of the field of view‘of the instrument.

(ii) Suppose that the length between the centres of the markson the lath is less than it should be by x /iooo of a metre (about1/25 of an inch). If the lath be set up 250 yards away from the

50

range-finderwhenadjustingfor coincidence,the resulting errorsin subsequentrange-takingwill be

Range measured R = 5,000 10,000 15,000 25,000Errors 50 200 45~ 1,250

30. This showshow seriousthe error in rangemaybecomeifan instrument is adjustedon a lath of incorrect length. It isthus important that the lath be kept in good condition andcheckedfrom time to time.

31. A changeof temperatureof about 440 F. will alter thelength betweenthe white marks by about the above amount(i/iooo metre), so adjustmenton the lath under extremesoftemperatureshouldbe avoidedasfar as is possible.

51

APPENDIX II

ADJUSTMENTS AND REPAIRS WHICH MAY BEUNDERTAKEN BY ARTIFICERS R.A. WHO HAVEPASSED A QUALIFYING COURSE IN ANTI-

- AIRCRAFT INSTRUMENTS

~. In addition to the adjustmentsdescribedin ChapterIII,minor mechanicalrepairs and adjustmentsare necessaryfromtime to time in order that the instrument may continue tofunction correctly. -

2. To carryout someof theseadjustmentseffectively,partialstripping of tile traversingor elevatingmechanismis necessary.

3. The adjustmentshave,therefore,beendescribedseparatelyfrom the processof dismantling.

To ELIMINATE BACKLASI-I BETWEEN THE TRAVERSING WORM

SPINDLE AND WORMWHEEL

4. Two smallspannerswill be requiredto fit tile headof thescrew (59), Fig. io, and the lock nut. Providing that thefriction ring (iii), Fig. 12, has been correctly adjusted (see

p. 33), any backlashbetween the spindleand wormwheelcanbetakenup by adjusting thescrew(5~),Fig. 10, until therotatingheadof the mounting respondsto the slightestmovementof thetraversing handwlieel (24), Fig. 8. The adjustingscrew shouldthenbe securedby meansof the lock nut. Careshouldbe takenthat the worm spindle is not set too deeply in mesh with tilewormwheel,otherwisethe traversinghandwheelwill be very stiffto turn, and the taperedkeeppins maybe broken.

To ELIMINATE BACKLASH BETWEEN THE ELEVATING WoRMSPINDLE AND WORMWHEEL

5. This adjustmentis performedby the adjustingscrew (12),Fig. 9, which regulatesthe depthof the worm spindlein meshwith the wormwheel (63), Fig. 9. It should be carriedout inconjunctionwith the adjustmentof the friction ring (64), PlateIII, on the left of the left bearingof the range-finder,themove-ment of which is controlledby five adjustingscrews. After thefriction ring has beencorrectly adjusted (see p. 34) the wormspindleis adjustedby meansof the screw (12), Fig. 9, until theinstrument respondsto the least movement of the elevatinghandwheel. The adjusting screw should finally be clampedby meansof the lock nut.

52

To DISMANTLE, CLEAN AND ASSEMBLE THE 1~0TATINGIIEAD

6. Unscrewthe two securingscrews(22), Fig. 12, andremovethe range-finderfrom the rotating headandsupport it on “V”blocks. -

7. Removethe nut andwasher(114), Fig. 12, clampingtheazimuth scale. Remove the scale. Releasethe lock nut andunscrewthe adjusting screw (59), Fig. 10, removethe bracketandpositionthe spindleball bearingsoas to throw the spindleout of gearwith the wormwheel. Removethe six screwsfromthe undersideof the rotating head, and removethe rotatinghead. Removethe keep screw securing the brassnut to thewormwheel bearing plate (112), Fig. 12, and unscrew therotating headpivot nut (109), Fig. iz. Removethesix screwsadjustingtile friction ring (~~i),Fig. 12, andalsothe ring andwormwheel (ilo), Fig. 12. Remove the wormwheel bearingplate (112), Fig. 12. The remaining portion of the rotatingheadcan now be removedfrom the main pivot. Removetheball bearing(113), Fig. 12. Removethe pivot screwsof thegimbal ring (104), Fig. 12, and tripod head (106), Fig, 12,marking them to guide replacement. All the parts should bethoroughly cleanedand lubricated,special attention being paidto the cleanlinessof the main pivot and bearing, the oil channel,The ball bearing and the gimbal screw bearings.- When replacingthe wormwheelbearingplate, it is most essentialthat it shouldbe agood fit on the main pivot, otherwisetherewill bebacklash.Any playmust,therefore,betakenup by insertingametalpackingbetweenthepivot andwormwheelbearingplate. Theremainderof the rotating headcannow be assembledandthe friction ringadjustedas alreadydescribed.

To DISMANTLE, CLEAN AND ASSEMI3LE THE TRAvERsING GEAR

8. Knockout thepin from thebottomof thehandwlieelshaft.Removethe small collar andslide the handwheeloff the shaft.Removethe keepscrewfrom the lower bearingscrewedcollar,and by means of the tool, Mark II No. 2 height and range-finder, unscrewthe collar. Removethe two-speedgearcomplete.Unscrewthe cap from the worm spindleshaft casing. Removetile keeppin, securingthe bevelwheel to the worm spindle (95),Fig. 10. Removeball bearingand worm spindle. Clean allparts and suitably lubricate. Examine the various keep pinsandreplaceif necessary. Assemblethe partsandfinally adjustfor backlash,asdescribedabove.

To REMOVE THE FRICTION RING, THE ELEVATING WORM SPINDLEBRACKET AND THE WORMWHEEL FOR CLEANING PURPOSES

9. Remove the five friction ring adjustingscrewsand slidethering alongthe tubeof therange-finder. Loosenthe lock nut,and unscrewthe adjustingscrew (12), Fig. 9, and removethebracketfrom theupperendof theworm spindlecasing. Positionthe upperball bearingof the worm spindle(78), Fig. 9, so that

53

time latter is disengaged from time wormwheel (63), Pig. 9.Remove the five screwssecuringthewormwheelbearing. Loosenthe keep screw from the fibre pointed friction screw (126), PlateII, and loosen the screw. Removethe bearing, and slide thisalso along the tube of the range-finder. The wormwheel is nowexposed and can be cleaned and lubricated. Replace the partsand adjust the friction bearing ring and worm spindle, as alreadydescribed.

To DISMANTLE AND ASSEMBLE THE WORM SPINDLE SHAFT OF THEELEVATING GEAR

10. Loosen the lock nut and unscrew the adjusting screw;remove the bracket from the upper end of time worm spindlecasing. Remove the elevating handwheel, as already described,for the traversing handwheel. Position the upper ball bearingof time worm spindle so that the latter is clear of the wormwheelteeth. Remove the keep screw from the lower bearing screwcollar, and by means of the tool, Mk. II No. 2 height and range-finder unscrew and remove the lower bearing. Remove the keepscrew from the upper end of the worm spindle and remove theworm spindle and two-speed gear. Clean all parts, examinekeep pins and renew if necessary. Lubricate and replace thespindle and gear. Adjust for backlash, as already described.

54

INDEXPAGE

A.Accuracy,effectof telescopicmagificationupon .... ... ... 7

,, of coincidencerange.finding... ... ... ... ... 44,, of height.finding ... ... ... ... ... ... 45

Achromatic,opticalsystem,definition of ... ... ... ... 13Adjustinghead,coincidence ... ... ... ... ... ... 17

,, - ,, halving ... ... ... ... ... ... ... 18lath, descriptionof ... ... ... ... ... ... 26

instructionsfor use ... ... ... ... .. 31Adjustment, coincidence ... ... ... ... ... .. 29

,, ,, exampleof observationsduring ... ... 30,, on an artificial infinity ... ... ... 31

onaninfinitely distantobject ... ... 31on a knownrange ... ... ... ... 31

halving ... ... ... ... ... ... ... 28,, of friction slip bearings ... ... ... ... ... 33

Adjustmentsthatcan be carriedout by artificers ... ... ... 52Advantages,of invertedstrip fleirl ... ... ... ... ... 13

this typeof instrument ... ... ... ... 6Aligning powerof theunaidedeye ... ... ... ... ... 43Angle of parallax,definition of ... ... ... ... ... ... S

,, ,, ,, effect on rangeof error in measuring ... ... 42Anglesof parallax, tableof, for variousranges ... ... ... 7Apex angle ... ... ... ... ... ... ... ... 5Application of the height andrange.findingprinciplesto the range-

finder ... ... ... ... ... ... ... ... ... 12Astigmatiserlenses ... ... ... ... ... ... ... 25

useof ... ... ... ,.. ... ... 25lever ... ... ... ... ... ... ... 18

Azimuth Scale ... ,.. ... ... ... ... ... ... 18slip bearing, adjustmentof ... ... ... ... ... 33

13.Backlash,elimination of, in elevatinggear ... ... ... ... 52

in traversinggear ... ... ... ... 52Base,virtual ... ... ... ... ... ... ... ... 7Bearingforks ... ... ... ... ... ... ... - ... 17Bearings,friction slip, adjustmentof ... ... ... ... ... 33

scaleof ... ... ... ... ... ... ... ... 18Binocular attachment ... ... ... ... ... ... ... 16Box, battery,switch andresistancecoil ... ... ... ... 19Bulb4volt”G” ... ... ... ... ... ... ... 20

C.

Careandpreservationof instrument ... ... ... ... ... 27Case ... ... ... ... ... ... ... . . . ... 20Cells, electric, inert “ 0 “ ... ... ... .. ... ... 20Centreprism combination ... ... ... ... ... ... 22Coincidence,adjustinghead ... ... ... .. ... ... 17

adjustment,bestobjects on which to make ... ... 31exampleof observationsduring ... ... 30

55 -

- PAGECoincidence,adjustment,methodsof effecting ... ... ... 30

principle ... ... ... .. ... ... ... 8prism ... ... ... ... ... ... ... 24range-finding,accuracyof ... ... ... ... 44

,, precisionof... ... ... ... ... 43theoryof ... ... ... ... ... 42

Consistency ... ... ... ... ... ... ... ... 44Correctionindicesfor height andrangescales... ... ... ... 21Cover,canvas,waterproof ... ... ... ... ... ... 27

D.Data,instrument ... ... ... •.. ... ... ... ... 3Deflectingprism ... ... ... ... ... ... ... ... 24Descriptionof heightandrange-finderandadjuncts ... ... 15Diopterscaleof range-findereyepiece ... ... ... 16Disadvantagesof this typeof instrument ... ... ... ... 6Dividing line ... ... ... ... ... ... ... ... 13Drill ... ... ... ... ... ... ... ... ... 35

E.

Elevatinggear ... ... ... ... ... ... ... ... 17adjustmentof friction slip bearing ... ... ... 34elimination of backlashin ... ... ... ... 52

Elevationscale ... ... ... ... .,. ... ... ... 17Equationsolvedby heightscalegear ... ... ... ... ... iiError in rangedueto error in measuringparallaxangle ... ... 42

of adjustment ... ... ... ... ... ... ... 44Errors,permissible,in height-finding ... ... ... ... ... 46,, ,, ,, ,, of singleobservation... ... 46

,, table of ... ... ... 48,, ,, ,, range-finding . .-. ... ... ... ... 44

- ,, ,, of singleobservation ... ... 45,, ,, table of ... ... ... 47

possible,in useof lath, adjusting ... ... ... ... 50Externalarrangementsof instrument ... ... ... ... ... 15Eye, aligningpower of ... ... ... ... ... ... ... 43Eyeguards ... ... ... ... ... ... ... ... 16, 19Eyepiece,range-finder ... ... ... ... .. ... ... 16

view—finder, focussingarrangementof ... ... ... 19

F.Field of view, appearanceof ... ... ... ... ... ... 13

,, ,, ,, ot range-finder ... ... ... ... ... ... 3of view-finder ... ... - ... ... ... ... 3

Focussingarrangements,of range-finder ... ... ... ... 16,, ,, of view-finder ... ... ... ... 19

Forks,bearing ... .. ... ... ... ... ... ... 17Formof recordfor use in trainingheight-takers ... ... ... 41Formula, range-finding ... ... ... ... ... ... ... 42Frames,long andshort ... ... ... ... ... ... ... 24

- G.Gear,elevating ... ... ... ... ... ... ... ... 17

heightscale... ... ... ... ... ... ... ... 20illuminating .,. ... ... ... ... ... ... 19

,, levelling ... ... ... ... ... ... ... ... 19,, traversing ... ... ... ... ... ... ,,. ... 17

56

PAGEGlass,halving ... ... ... ... ... ... ... ... 23Glasses,moderating ... ... - ... ... ... ... ... - 16

- object ... ... ... ..-. 24Graduationof azimuthscale-,.. ... .. - - ... - 18

- ,, - ,, elevationscale ... ... ... ... 17,, heightscale ... ... ... ... ... ... 22

- ,, ,, rangescale,external ... ... ... ... ... 22,,-,, ,, ,, internal .,. ... ... 23

H.Halving adjustinghead ... ... .-.. ... ... ... ... 18

adjustment,bestobjectson which to make ... - ... 29methodof effecting ... ... ... ... 29

- ,, effect of coincidenceadjustmenton ... ... 33glass ... ... ... ... ... ... ... ... 23testfor .,. ... ... ... ... ... 28

- I.19

- ... ... 3123

32223

~ 13

Lampsockets ... ... ...

Lath,adjusting,descriptionof ... ... -

- - ,, ,, errors,possible,in useof- ,, instructionsfor useof

theory of ...

Lenses,astigmatiser ... - ...

Levelling gear ... ... ...

Lever,astigmatiser ... ...

1826503149251918

Magnification, effect of oii accuracy ...

,, of telescopicsystem ...

of view-finder ... ... ..,

Mounting, TypeM.T. 12 .. - ... ...

Mounts,pentagonalprism ... ... - ... -

Movement,factorof ... ... ... ... - -

0.Objectglasses ... ... ... ... ...

Observations,exampleof, duringadjustment...- ,, - Iorm for recordingduringtraining

Opensights ... ... ... ... ... -

(711)

57

~. 2430

~.. 41.,. 16

Illuminating gear - ...

Infinity, artificial, adjustmentonmark on internalrangescale

~Instrument data ... ...

Internalarrangementsof instrumentInternal rangescale ...

Invertedstrip uI~1d - ... -

Ic.Known range,adjustmenton - 31

L. -

M..,. 7

33

19- ... 25

46

N. -

Notes on the training of height-takers. ... .,. - ... ,•. 39

I-,

Parallax angle ... ... ... ...

error in rangedueto error inangles,tableof for variousranges

Pentagonalprisms ...

Permissibleerrorsin height ... ...

of single observationtableof ...

range ...

,, of singleobservation,, ,, tablesof ...

Precisionof height-finding ... ...

,, ,, range-finding ... ...

Preservationandcareof instrument ...

Principle, coincidence ...

,, height-finding ... ...

,, range-finding ... ... ...

Prism, centrecombination ... ...

- ,, coincidence ... ... ...

deflecting ... ... ... ...

Prisms, pentagonal ... ... ...

Protector,sun, canvas ... ... ...

P.PAGE

542

725

- ... ... 4646484345474543278

116

2224242516

Q.Quadrantrack ... ... ... .., ... ... ... ... 17

- R.Rack,quadrant ... ... ...

Rangescale,infinity mark on ...

,, scales,graduationof ...

Range.finding,accuracyof ...

coincidence,theoryof,, precisionof ...

- ,, principle ... ...

Ray shades ... ... ...

S.Scale,azimuth ... ... ... ...

elevation ... ... ... ...

,, height ... ... ... ...

- ,, ,, graduationof ...,, rangeexternal ... ... ... ... -,, ,, ,, graduationof ...

,, ,, internal ...

graduationof ...

Shades,ray ... ... ... ...

Sights,open ... ... ... ...

Singleobservationof range, relianceto beplacedon,, ,, ,, heigl~t, ,, - ,,

Sockets,lamp ... ... ... ...

Stand ... ... ... .., ...

Strip field ... ... ... ... ...

- T.Tableof parallaxangles... - ... ...

permissibleerrorsin range ...

,, ,, ,, ,, in height ...

58 -

1723234442

- 436

16

181721222122232316164546181913

74748

Temperature,effect on lath,adjusting...Test for coincidence ,.. ... ...

halving ... ... ... ...

Theoryof coincidencerange-findingandheight-finding,, ,, lath, adjusting ... ...

Tool, Mark II No. 2 height andrange-finderTrainingof height-takers,noteson ..,

Traversinggear ~.. ... ...

,, ,, adjustmentof friction slip bearingelimination of backlashin

Tripod, head, mounting ... ... ...

,, stand ... ... ... ...

PAGE513028424953391733521919

View-finder, alignmentofdescriptionof

Virtual base ... ...

- W.Window, internalrangescaleWindows,end ... ...

heightandrangescalesWorkinghead ... ...

33187

102118

Printedunderthe authority of HLs MAJESTY’S STATI0~ERYO,rrcg,By Wyman& Sons,Limited, FetterLane, London,E.C. 4.

711, ‘Vt- 12158—743/745. 2,500. 1/27. Wy. & S., Ltd. Op. 64. P. 26j74~.