Oiml Bulletin July 2001

been granted such certificates, may be found on the OIMLweb site and information is also published in theAssessment of OIML Activities (see page 43).

However, major improvements still have to be madeover the next few years, in particular:

K To simplify the certification of families of measuringinstruments, i.e. instruments from the same manu-facturer, based on the same technology and differing onlyin certain characteristics (e.g. the maximum capacity) inwhich case it is not necessary to repeat all the tests on allthe instruments belonging to the family.

K To develop the certification of modules, e.g. indicatingdevices, sensors and electronic equipment, with a view tofacilitating the certification of an instrument made up ofcertified modules.

K To develop the certification (in fact the initial verifica-tion) of mass-produced instruments, since up to now theOIML Certificate System applies to types (patterns) ofinstruments.

K Above all, the objective is to develop multilateral agree-ments of recognition of test results associated with OIMLcertificates in order to eliminate multiple testings andthus apply the WTO directives concerning testing in thelegal metrology field.

This is the responsibility of the OIML TechnicalSubcommittee TC 3/SC 5 under a joint USA/BIML secre-tariat and significant progress in this field is expected to bemade by the end of 2002. This activity is conducted takingdue consideration of the views of certification bodies as wellas those of manufacturers of measuring instruments, and inline with the general principles on conformity assessment,testing and accreditation developed within the WTO,ISO/CASCO, ILAC and IAF. K

Launched in 1991 following several years of reflectionwithin the OIML culminating in a decision made bythe International Committee of Legal Metrology, theOIML Certificate System for Measuring Instruments is nowten years old.

Initial developments were very slow and in fact the firstcertificate was not issued until 1992. Over the following twoyears, the number of certificates issued only just exceeded20 (in 1993) and 40 (in 1994). However from 1995 on therewas a significant acceleration and one decade later thenumber of certificates issued annually now exceeds 100, asmay be seen from the bar chart on the front cover of thisBulletin.

A number of other key figures also illustrate the growingsuccess of this activity:

K Some 20 OIML Member States (out of 57) have nowestablished national authorities for issuing OIMLcertificates, and a number of other Member States areconsidering doing likewise.

K More than 30 categories of measuring instruments(weighing devices, fuel dispensers, clinical thermo-meters, breath analyzers, etc.), may receive OIMLcertificates and this number is progressively increasingwith the issuing of new or revised Recommendationsapplicable within the System.

K Over 200 manufacturers or importers of measuringinstruments from some 30 countries have successfullyapplied for OIML certificates.

K More and more countries accept OIML certificates andassociated test results to accelerate and facilitate thegranting of national or regional type approvals.

More detailed statistics concerning certificates issued,including information on those manufacturers that have

K Editorial

Ten Years of OIML Certification

BIML

Abstract

For a given error distribution, confidence in the measure-ment process depends on the test uncertainty ratio (TUR)and on the confidence interval. When selecting ameasuring instrument or measurement standard to carryout a calibration or verification or, in general, a meas-urement, this dependence becomes a vital issue.

The author has considered the effect of several TURsencountered in practical situations on incorrect testdecisions. This consideration has also been extended tothe effect on correct test decisions, reliability of test resultsand confidence in the measurement process for normalerror distribution, for both the equipment under test(EUT) and the calibrating instrument, at two confidenceinterval specifications.

This paper contains a short presentation of specificrelevant definitions and issues, results of the study anddiscussion, and two examples of a lack of specificinformation on the TUR in certain standards. The analysishas been performed for TURs ranging from 1:1 to 100:1and for confidence interval specifications of 2s and 3s .

Both the information given and the conclusions whichhave been drawn can be used in calibration and verifica-tion and, generally, also in measurement.

1 Introduction

Measurements and the calibration of measuring instru-ments are essential aspects of activities such asmaintaining quality control and quality assurance inproduction, complying with and enforcing laws and

regulations, conducting research and development inscience and engineering and calibrating and verifyingmeasurement standards and instruments in order toachieve traceability to national standards.

Calibration is the determination, by measurementand comparison with a measurement standard, of thecorrect value of a reading on a measuring instrument.The calibration system considered in this paper isshown in Fig. 1. The calibrator (standard) is the sourceof the standard signal, and the standard value of thecalibrator is compared with the measurement resultindicated by the EUT.

Verification is an activity performed by a nationalmeasurement service in which similar measurementprocedures are used as for calibration.

The overall measurement error consists of twocomponents: the error arising in the EUT and thatoriginating from the measurement standard [1]. It isworth mentioning that good measurement has itsorigins as much in the study of errors or uncertainties ofthe measurement as it does from the choice of theprinciple of measurement [2]. When reporting the resultof a measurement of a physical quantity, it is thereforealso necessary to state the relevant error or uncertaintyof the measurement.

Uncertainty of measurement is a parameter associ-ated with the result of a measurement that characterizesthe dispersion of the values that would reasonably beattributed to the measurand [3].

Figure 2 illustrates the meaning of uncertainty anderror of measurement using the normal distributioncurve and shows a situation where the confidenceinterval ranges from 2s to + 2 s which corresponds toan uncertainty of 2s at about 95.45 % confidence level,where s is the standard deviation. In metrologicalpractice the confidence interval is usually assumed to befrom 2 s to + 2s or from 3 s to + 3s [3, 4]. In Fig. 2,the true value is 1s and the EUT reading is 0, so theerror is + 1s .

5O I M L B U L L E T I N V O L U M E X L I I N U M B E R 3 J U LY 2 0 0 1

t e c h n i q u e

UNCERTAINTY

Uncertainty of thecalibrating instrument,confidence in themeasurement process andthe relation between them

TADEUSZ SKWIRCZYNSKIIndependent Consultant, Warsaw, Poland

Calibrator (test signal) EUT

EUT reading

Fig. 1 Measurement system used in calibration

6 O I M L B U L L E T I N V O L U M E X L I I N U M B E R 3 J U LY 2 0 0 1

t e c h n i q u e

Fig. 2 Error and uncertainty

Fig. 3 Illustration of incorrect test decisions for 2s specifications for calibrator and EUT and normal distribution of errors in their populations


t e c h n i q u e

2 Test uncertainty ratio (TUR)

The TUR for a measurand is defined as the standarduncertainty of the EUT divided by that of the calibratinginstrument (measurement standard) used to test it [4, 5,6]. A reliable TUR is only obtained when thespecifications for the EUT and the calibratinginstrument are correlated according to their errordistributions and confidence intervals. It can be saidthat a reliable TUR is a sine qua non condition for goodquality calibration. The purpose of calibration is to gainconfidence that the EUT is capable of makingmeasurements within the specifications. And, generally,the purpose of measurement is to gain confidence thatthe value of the measurand is within its tolerance limits.Testing laboratories need to use measuring instrumentsthat have uncertainty specifications which are adequatefor the measurements they perform.

3 Incorrect test decisions and confidence inthe measurement process

Actual measuring instrument test results can containfour kinds of test decisions:

acceptance of good units, rejection of bad units, rejection of good units, and acceptance of bad units.

The ideal situation is that the results consist ofonly the first two kinds of test decisions, the second twobeing the results of uncertainty in the specifications forboth the EUT and the calibrating instrument.

An accepted good unit is a calibrated instrumentthat is within its specified tolerance limits and a rejectedbad unit is one that is outside its tolerance limits.Thus, the actual test results contain correct andincorrect test decisions. Correct test decisions containacceptance of good units and rejection of bad unitswhereas incorrect test decisions contain rejection ofgood units (incorrect fail) and acceptance of bad units(incorrect pass). This situation is shown in Fig. 3 for a5:1 TUR, normal error distribution and 2s specificationsfor both the EUT and the measuring instrument(calibrator). In this example, the normal distributioncurve N (0, 1) - where 0 is the mean value and 1 is thestandard deviation - illustrates the error distribution forthe calibrator and the normal distribution curve N (2, 5)shows the error distribution for the EUT.

As illustrated, the actual output of the calibrator islarger than the nominal output by the maximumpermissible error, i.e. by + 2s . Relative to the EUT

specification, the calibrator output is at + 0.4s . In termsof the test limits, the EUT readings which are trulywithin the tolerance limits are in the range from 1.6sto + 2.4 s . This is due to the fact that the readings have anormal distribution and so they are symmetricallydistributed on either side of a stimulus that is displacedby + 0.4 s from its nominal value. That is why the EUTreadings between + 2s and + 2.4 s will be incorrectlyoutside the tolerance limits and the readings between 2s and 1.6 s will be incorrectly within them. As thedistribution of errors is normal, the number of EUTunits within the tolerance limits that are incorrectlyrejected exceeds the number of EUT units which areoutside the tolerance limits that are incorrectlyaccepted.

Furthermore, as the error distribution is normal sothe curve is symmetrical, and analogous results of theanalysis will be obtained when the output of thecalibrator is displaced to 2s , i.e. to 0.4s relative to theEUT specification.

The decimal fraction of correct test decisions equals1 minus the decimal fraction of incorrect test decisions(incorrect fail plus incorrect pass). The larger is thefraction of correct test decisions, the larger will be theconfidence in the measurement process. It is generallyassumed that 100 % correct test decisions is unat-tainable at any cost. On the other hand, there is usuallya target value for the correct test decision percentage.This percentage depends on the activity supported bythe testing. The percentage of correct test decisionsbelow the target value will significantly decreasereliability of test results and confidence in themeasurement process and may be assumed to haveunacceptable effects on such factors supported by thetest as human health, safety and lives, and cost ofmanufacturing or quality of product, to mention just afew of them.

4 Results of analysis and discussion

The incorrect test decisions have been studied as afunction of the TUR value ranging from 1:1 to 100:1 at2 s and 3 s confidence intervals and normal errordistribution for both the EUT and the calibrator.

The results of the study are given in the form ofgraphs in Figs. 47. The graphs contain the error of thecalibrator in standard deviations, as an independentvariable, and the following decimal fractions of the EUTpopulation as dependant variables:

good units rejected (incorrect fail units) in Figs. 4and 6, and

bad units accepted (incorrect pass units) in Figs. 5and 7.


t e c h n i q u e

Fig. 4 Distribution of incorrect fail test decisions as a function of calibrator error for 2 s specifications

Fig. 5 Distribution of incorrect pass test decisions as a function of calibrator error for 2 s specifications

Fig. 6 Distribution of incorrect fail test decisions as a function of calibrator error for 3 s specifications

Fig. 7 Distribution of incorrect pass test decisions as a function of calibrator error for 3 s specifications


t e c h n i q u e

Graphs 4 and 5 refer to 2s specifications and graphs6 and 7 refer to 3s specifications for both the EUT andcalibrator populations and normal distribution in theEUT population. The curves given in Figs. 47 refer tothe following TUR values (curves from top to bottom):1:1, 1.5:1, 3:1, 4:1, 5:1, 10:1, 20:1, 100:1. The incorrectfail unit fraction and incorrect pass unit fraction of theEUT population can be obtained from relevant values ofthe cumulative distribution function. It can be seen fromthe data in the Figures that the percentages of incorrecttest decisions, and thus the percentage of correct testdecisions, depend strongly on the TUR value and theconfidence interval. The percentage of correct testdecisions increases when the TUR or confidence intervalincreases.

But increasing the TUR requires the use of measur-ing (calibrating) instruments of higher accuracy, whichcan be more costly. An increase in the confidence inter-val increases the uncertainty of measurement. As long asthe minimum TUR is met or exceeded, the uncertaintiesof the measurement standard when assigning anuncertainty to the calibration can be ignored.

The results of analysis indicate that 2s confidenceinterval specifications require a much larger TUR valuethan 3 s confidence interval specifications in order toensure the same percentage of correct test decisions. Forexample, assuming the 3:1 TUR, the percentage of in-correct fail test decisions is circa 6.85 % (see Fig. 4) andthe percentage of incorrect pass test decisions is circa1.89 % (see Fig. 5) for 2s specifications when the cali-brator output is just within specifications at the 2slimit. For the same TUR, the percentage of incorrect failtest decisions is circa 2.14 % (see Fig. 6) and the per-centage of incorrect pass test decisions is circa 0.13 %(see Fig. 7) for 3s specifications when the calibratoroutput is just within specifications at the 3s limit.

It is necessary to increase the TUR more than twotimes, i.e. to more than 6:1 for 2s specifications if thepercentage of incorrect fail test decisions is not toexceed 2.14 % too. The percentage of incorrect pass testdecisions circa 0.13 % for 2s specifications is at circa85:1 TUR. The last condition requires using veryaccurate measurement standards to perform the meas-urement.

In some cases it is possible to find measuredinstruments with the uncertainty being de facto nearlythe same as the uncertainty of the calibrating instru-ment used to calibrate them, i.e. the TUR is about 1:1. Inthe case of 2s specifications, taking into considerationthe data from Figs. 4 and 5 for 1:1 TUR, one can say thatabout 50 % of test decisions would be incorrect, i.e.about 47.7 % of the good EUT units would be rejected(Fig. 4) and about 2.27 % of the bad EUT units would beaccepted (Fig. 5), when the calibrator output is justwithin specifications at the 2s specification limit.Similarly, in case of 3s specifications, the percentage of

incorrect test decisions would be about 50 % too, i.e.about 49.8 % of the good EUT units would be rejected(Fig. 6) and about 0.14 % of the bad EUT units would beaccepted (Fig. 7), when the calibrator output is justwithin specifications at the 3s specification limit. Asone assumes normal error distribution in the calibratorpopulation, about 2.28 % of that population for 2sspecifications and about 0.14 % for 3s specificationswill fall under this condition.

There are some practical activities in science andtechnology fields where TUR values as large as 100:1 arerequired. Such TUR values enable a high reliability oftest results and high confidence in the measurementprocess to be obtained. In such cases the percentage ofincorrect test decisions would be as low as about 0.22 %when the calibrator error is just within specifications atthe 2s specification limit (see Figs. 4 and 5) for 2sspecifications and incorrect test decisions as low asabout 0.027 % when the calibrator error is just withinspecifications at the 3s specification limit (see Figs. 6and 7) for 3s specifications.

5 Two examples of a lack of specificinformation on the TUR

A lack of adequate or complete specific information onthe TUR can be noticed even in some official documentsand measurement procedures. In effect, in such casesinexperienced persons can have some difficulties inmaking proper measurements. For illustration, twoexamples concerning measurement uncertainty require-ments of standards are discussed below.

ISO 10012-1 standard [7]

The requirements on the TUR arise from clause 4.3 ofthis standard, which reads: The error attributable tocalibration should be as small as possible. In most casesof measurement, it should be no more than one thirdand preferably one tenth of the permissible error of theconfirmed equipment when in use. If normal errordistribution is assumed for both the EUT and thecalibrating instrument then the TUR is 3:1 for the lowerpermissible limit of error ratio, according to the above-mentioned requirements of the standard.

Thus, even for 3s specifications (see Figs. 6 and 7),there will be about 2.28 % of incorrect test decisionswhen the calibrating instrument error is just withinspecifications at the 3s specification limit, and asmuch as about 8.7 % of incorrect test decisions for 2s

specifications (see Figs. 4 and 5) when the calibratinginstrument error is just within specifications at the 2sspecification limit.

IEC 60373 [8] and IEC 60645-1 [9] standards

The requirements on measurement uncertainty for themechanical coupler arise from clause 5.1 of IEC 60373,which reads: The calibration uncertainty shall notexceed 1.0 dB for frequencies up to and including 2 kHznor shall it exceed 2 dB for frequencies up to andincluding 8 kHz. The mechanical coupler is a piezo-electric transducer, which is used in calibrating thestimulus level of the audiometer bone conduction. Thempe for the stimulus level of the audiometer is 3 dBfor frequencies up to and including 4 kHz [9].

Assuming normal error distribution for the stimuluslevel for both the audiometer and mechanical couplerone has a 1.5:1 TUR value at 3 kHz. At this frequency,taking into consideration results of the analysis givenabove (see Figs. 47) one can draw the followingconclusions. If the mechanical coupler used forcalibration of audiometers and the audiometers arecalibrated according to these standards, there will beabout 15.9 % of incorrect audiometer test decisions for3s specifications, i.e. 15.9 % of incorrect rejections orincorrect acceptances of audiometers, when the error ofthe mechanical coupler is just within specifications atthe 3s specification limit and as much as about 25.2 %of incorrect audiometer test decisions for 2s specifi-cations when the error of the mechanical coupler is justwithin specifications at the 2s specification limit.

6 Conclusions

Results of the study indicate the way in which the TURand confidence interval affect the incorrect testdecisions and thus the correct test decisions, reliabilityof test results and confidence in the measurementprocess.

Larger TUR values and confidence intervals signifylower percentages of incorrect test decisions, higherreliability of test results and higher confidence in themeasurement process.

But larger TUR values require the calibratinginstrument to be of higher accuracy, which usuallyimplies a higher cost. A larger confidence intervalsignifies a higher uncertainty of measurement.

As long as the minimum TUR is met or exceeded, atan assumed value of confidence interval, the uncertain-ties of the measurement standard (or, generally, of themeasuring instrument) when assigning an uncertaintyto the calibration or measurement can be ignored. K

7 References

[1] Finkelstein, L., Grattan, K.T.V., Eds., ConciseEncyclopedia of Measurement & Instrumentation,Oxford, New York, Seoul, Tokyo, Pergamon Press,1994

[2] Sydenham, P.H., Ed., Handbook of MeasurementScience, Vol. 1, Chichester, New York, Brisbane,Toronto, Singapore, John Wiley & Sons, 1982

[3] International Vocabulary of Basic and GeneralTerms in Metrology (VIM), BIPM, IEC, IFCC, ISO,IUPAC, IUPAP, OIML - ISO, Geneva, 1993

[4] Guide to the Expression of Uncertainty in Meas-urement (GUM), BIPM, IEC, IFCC, ISO, IUPAC,IUPAP, OIML - ISO, Geneva, 1995 (Corrected &reprinted edition)

[5] Turzeniecka D., Study of Results of Comparison ofSelected Uncertainties, Metrology and MeasuringSystems, Vol. V, 1-2, PWN, Warsaw, 1998

[6] Calibration: Philosophy in Practice, 2nd Ed., FlukeCorporation, 1994

[7] ISO 10012-1, Quality assurance requirements formeasuring equipment-Part 1: Metrological con-firmation system for measuring equipment, ISO,Geneva, 1993

[8] IEC 60373, Mechanical coupler for measurementson bone vibrators, IEC, Geneva, 1990

[9] IEC 60645-1, Pure-tone audiometers, IEC, Geneva,1992


t e c h n i q u e

TADEUSZ SKWIRCZYNSKI

Independent Consultant,Warsaw, Poland

The author welcomes comments from readers and may be contacted by e-mail: [email protected]

Abstract

The provision of the mass scale below one kilogram isachieved by subdivision. This paper describes one of themethods used by INM including details of the weighingtechniques, weighing schemes, equipment used and theuncertainty of measurement of all the standards involved.

1 Introduction

INM is the custodian of the Prototype Kilogram No. 2.As such, it is INMs task to propagate the Romanianmass scale by subdivision and multiplication of thekilogram.

Class E1 weights ensure traceability to the nationalmass standard (the value of which is derived from theInternational Prototype of the kilogram, maintained bythe BIPM) and weights of Class E2 and lower [1]. Theyare used as standards at the thirteen Romaniancalibration laboratories.

2 Test procedures

The set (500...1) g of Class E1 weights usually has thefollowing composition:

500 g, 200 g, 200* g, 100 g50 g, 20 g, 20* g, 10 g

5 g, 2 g, 2* g, 1 g

The 1 kg reference standard, of known mass, is usedfor calibration. Mass determinations are carried out bysubdivision (to link standards having different nominalvalues up with a reference standard). Depending on theweighing scheme, this procedure requires a specificminimum number of standards. By the method of leastsquares adjustment, the mass departures and theirstandard deviations are calculated.

Weighing is always carried out as substitutionweighing, i.e. single weights or combinations are alwayscompared with another combination of the samenominal value. The difference between the balanceindications has the symbol D m and it is necessary toapply air buoyancy corrections to the observed weighingdifferences.

If y is the new corrected difference, this gives:

y = D m + ( r a r o)(V1 V2) (1)

where:

y is the corrected indication;D m is the difference in balance readings calculated

from one weighing cycle (RTTR, where R is thereference standard and T is the test weight);

r o = 1.2 kg m-3, the reference air density;

r a = air density at the time of the weighing; andV1, V2 are the volumes of the standards (or the total

volume of each group of weights) involved in themeasurement.

In designing the scheme, all the masses from 1 kg to1 g are broken down into decades. A weighing schemewith 12 equations per decade is used in the calibration[1]. The first decade includes the 1 kg standard.

For subsequent decades the role of the standard istaken by the 1 from the previous decade; thus the100 g, 10 g masses become intermediate standards,whose uncertainty is propagated directly to masses inthe decade they head and hence to those in subsequentdecades.

With the reference standard, the mass havingnominal values: 500 g, 200 g, 200* g, 100 g, S 100 g (thesum of 50 g, 20 g, 20* g and 10 g from the next decade)shall be calibrated using a 1 kg mass comparator. Theobservations are of the same accuracy (for all masscomparisons the same balance was used in the firstdecade).

Once all the weighings have been completed, the firststep consists in the formation of the design matrix.

Matrix X contains the information about theequations used (the weighing scheme) and matrix Ycontains the measured differences from these equations.


t e c h n i q u e

WEIGHTS

Test procedures for Class E1weights at the RomanianNational Institute ofMetrology: Calibration ofmass standards by sub-division of the kilogram

ADRIANA VLCU, Romanian Bureau of LegalMetrology, National Institute of Metrology,Romania

Denote:

X = (xij);i = 1...n;j = 1...k;xij = 1, 1 or 0;b is (b j) vector of unknown departures; andY is (yi) vector of measured values (including buoyancy

corrections).

1000 g 500 g 200 g 200* g 100 g S 100* g

The first row of the matrix represents difference inmass between the +1 and the 1 weight, for example:(500 + 200 + 200* + 100) 1000 = y1

If (XT X) is the matrix of the normal equations, thisgives:

(XT X) b = XT Y (2)

where XT is a transpose of X:

The next step introduces two matrices: (XT X)-1 istermed the inverse of (XT X) and the product (XT X)-1XT.

The matrix design contains only the weighingequations. For this reason, the system can not be solvedbecause the determinant of (XT X) is zero and theinverse (XT X)-1 does not exist.

To overcome this problem the Lagrangian multi-pliers method is applied [3, 4] which consists of addingthe reference standard (restraint mR) to the vector Y,the Lagrangian multipliers l to the vector b , a linek + 1 and a column k + 1 (both containing the elements1,0,1) to the normal equation and to the matrix XT asfollows:


t e c h n i q u e

1 1 1 1 1 01 1 1 1 0 10 1 1 1 1 00 1 1 1 0 10 0 1 1 1 10 0 1 1 1 10 0 1 1 1 10 0 1 1 1 10 0 1 0 1 10 0 1 0 1 10 0 0 1 1 10 0 0 1 1 1

X =

1 1 0 0 0 0 0 0 0 0 0 01 1 1 1 0 0 0 0 0 0 0 01 1 1 1 1 1 1 1 1 1 0 01 1 1 1 1 1 1 1 0 0 1 11 0 1 0 1 1 1 1 1 1 1 10 1 0 1 1 1 1 1 1 1 1 1

XT =

2 2 2 2 1 12 4 0 0 0 02 0 10 0 0 02 0 0 10 0 01 0 0 0 10 01 0 0 0 0 10

XT X =

y1y2y3y4y5y6y7y8y9y10y11y12

Y =

y1y2y3y4y5y6y7y8y9y10y11y12mR

Y =

b 1b 2b 3b 4b 5b 6

b =

2 2 2 2 1 1 12 4 0 0 0 0 02 0 10 0 0 0 02 0 0 10 0 0 01 0 0 0 10 0 01 0 0 0 0 10 01 0 0 0 0 0 0

XT X =

The last column and row contains the factorhj = mj/mr, the ratios between the nominal values of theunknown weights (mj) and one of the reference (mr).

The best estimate of b , b for an over-determinedsystem of equations X is given by:

b = (XT X)-1 XT Y (3)

3 Example of a least-squares analysis:Equipment, standards and results

3.1 Equipment

The balances used in the measurements in the rangefrom 1 g to 500 g are listed below:

Type Max Standard Indicationdeviation, mg

AT 1005(Mettler) 1 kg 0.01 0.02 Digital

H20(Mettler) 160 g 0.01 Optical

2405(Sartorius) 30 g 0.002 Optical

Additionally, the mass laboratory is equipped withinstruments to measure:

the pressure, measured using a standard barometer(U = 2 mbar, k = 2);

the relative humidity, measured using a standardpsychrometer (U = 3 %, k = 2); and

the temperature, measured using a standard thermo-meter (U = 0.4 K, k = 2).

From the air parameters, the air density is calculatedusing the equation recommended by the CIPM [2].

3.2 Standards

The 1 kg reference standard is used as the known massfor the calibration, where:

V = 127.7398 cm3, expanded uncertainty Uv = 0.0024 cm

3, k = 2. conventional mass mcr = 0.999 996 891 kg,

expanded uncertainty U(mcr) = 0.044 mg, k = 2.

The observed mass differences read:

The vector b with the unknown masses, accordingto equation (3) above, gives:


t e c h n i q u e

1 1 0 0 0 0 0 0 0 0 0 0 01 1 1 1 0 0 0 0 0 0 0 0 01 1 1 1 1 1 1 1 1 1 0 0 01 1 1 1 1 1 1 1 0 0 1 1 01 0 1 0 1 1 1 1 1 1 1 1 00 1 0 1 1 1 1 1 1 1 1 1 00 0 0 0 0 0 0 0 0 0 0 0 1

XT =

0 0 0 0 0 0 10 1/4 0 0 0 0 1/20 0 1/10 0 0 0 1/50 0 0 1/10 0 0 1/50 0 0 0 1/10 0 1/100 0 0 0 0 1/10 1/101 1/2 1/5 1/5 1/10 1/10 0

(XT X)-1=

b 1b 2b 3b 4b 5b 6l

b =

3.7803.3911 0.04 0.050.010.010.0250.0280.0170.0170.0200.022

3.109

Y =

1000 g 3.109 mg500 g + 0.115 mg200 g + 0.075 mg200 g + 0.061 mg100 g + 0.020 mgS 100 g + 0.029 mg

b =

The inverse of XT X will be:

The value assigned to the summation S 100 g by thefirst decade constitutes the restraint for the seconddecade with the individual weights in the summationbeing calibrated separately in the second series. Thesummation of weights S 10 g becomes the restraint forthe third decade. Then, the same procedure is used forthe second and the last decades.

4 Analysis of uncertainties

4.1 Type A uncertainty

If the adjusted mass difference of the weighingequations is Y = X b , the residual for each equationis calculated as follows:

e = Y Y (4)

The calculation of e for the example gives theresults:

The standard deviation s of the observations iscalculated by:

The residuals res. are the elements of the vector e ;n = n k + 1 represents the degrees of freedom (n kis the difference between the number of performedobservations and the number of unknown weights; 1 isthe number of the restraints). According to this equationthe standard deviation is:

s = 0.007 mg

The variance covariance matrix for b is given by:

Vb

= s2(XT X)-1 (6)

where the variances on the values of the solutions b aregiven by the diagonal elements of the matrix (XT X)-1

denoted by cij. The off-diagonal elements of the matrixgive the covariance between the weights.

The standard deviation (uncertainty of type A) of aparticular unknown weight is:

The random uncertainty uA( b j) has a local com-ponent arising from measurements in the currentdecade and after the first decade, a propagatedcomponent arising from random uncertainty in theintermediate standards.

4.2 Type B uncertainty

The components of type B uncertainties are:

4.2.1 Uncertainty associated with the referencestandard

where hj is described above.


t e c h n i q u e

2 10-3

2.1 10-3

10 10-4

05 10-3

5 10-3

2 10-3

5 10-3

9 10-3

9 10-3

8 10-3

8 10-3

e =

00.00350.00220.00220.00220.0022

mguA( b j) = s cij =ABB

0.02200.01100.00440.00440.00220.0022

mg (7)ur ( b j)= hj umcr =

0 0 0 0 0 0 10 1/4 0 0 0 0 1/20 0 1/10 0 0 0 1/50 0 0 1/10 0 0 1/50 0 0 0 1/10 0 1/100 0 0 0 0 1/10 1/101 1/2 1/5 1/5 1/10 1/10 0

Vb

= 0.000049

res2iABBBBni=1S

1n

s = (5)

4.2.2 Uncertainty associated with the air buoyancycorrections

ub2

(b j) = (Vj hjVr)2

u2r a + ( r a r o)

2(u2Vj + hju2Vr) (8)

where:

Vj ,Vr = volume of test weight and referencestandard, respectively;

u2r a = uncertainty for the air density;

r o = 1.2 kg m-3 is the reference air density;

u2Vj , u2Vr = uncertainty of the volume of test weight

and reference standard, respectively.

4.2.3 Uncertainty due to the display resolution of a digital balance

For the first decade where a digital balance with thescale interval of d = 0.01 mg is used, the uncertainty dueto resolution is [1]:

(9)

4.3 Combined standard uncertainty

The combined standard uncertainty of the conventionalmass of the weight b j is given by:

uc( b j) = [uA2(b j) + ur

2( b j) + ub

2(b j) + ud

2 ] 1/2 (10)

The summation contains all the contributions des-cribed above.

4.4 Expanded uncertainty

The expanded uncertainty U (with k = 2) of the con-ventional mass of the weights b j is as follows [8]:

5 Uncertainty budget for the first decade

Table 1 on page 16 shows the results obtained from theleast squares analysis of the weighing data and theirassociated uncertainties. It also lists the contributiondue to the uncertainty in the value of the standard, in thebuoyancy correction and in the balance.

6 Conclusions

A calibration scheme for mass standards below 1 kg hasbeen described. The whole set of masses is calibrated,decade by decade, in terms of a 1 kg standard.

The test procedure described leads to an efficientcalibration of sets of class E1 weights, also used tocalibrate laboratory standards with lower uncertainty.

The subdivision weighing scheme and the electronicmass comparator used lead to an appreciable reductionin uncertainty in each mass value, compared withprevious calibrations.

One way to reduce the uncertainty and to obtainbetter results is to use balances of much greater ac-curacy and in near perfect environmental conditions. K

Table 1 and References on page 16


t e c h n i q u e

00.00300.00110.00110.00060.0006

mgub(b j) =

0.04400.02520.01280.01280.01020.0102

0.0440.030.010.010.010.01

mg (11)=U = k uc(b j) =

0.02200.01260.00640.00640.00510.0051

mguc(b j) =

! 2 = 0.0041 mg

d / 2

3ud = ABAB

References

[1] OIML: International Recommendation R 111, Weights of classes E1, E2, F1,F2, M1, M2, M3 (OIML, 1994)

[2] BIPM: Formule pour la dtermination de la masse volumique de lairhumide (1991)

[3] Schwartz, R.: Realization of the PTBs mass scale from 1 mg to 10 kg, PTB MA-21e /1991

[4] Schwartz, R.: Guide to mass determination with high accuracy. PTB MA-40 /1991

[5] Romanowski, M.: Basic theory of the calibration of mass standards[6] Riety, P.: Quelques nouveaux aspects sur ltalonage des botes de masses en

srie ferme. BNM No 60 /1985[7] Vlcu, A: Greutat, i etalon cl.E1, INM 1995[8] Benoit, J.M.: Ltalonnage des sries de poids, Travaux et Mmoires du

BIPM, Tome XIII, 1907[9] Stuart Davidson and Sylvia Lewis: Uncertainties in Mass Measurement.

NPLs analysis of data from the calibration of weight set NPLW 43. EurometProject No 231/1992

[10] Guide to the Expression of Uncertainty in Measurement (GUM): BIPM, IEC,IFCC, ISO, IUPAC, IUPAP, OIML - ISO, Geneva, 1995 (Corrected & reprintededition)

ADRIANA VLCU,Romanian Bureau of

Legal Metrology,National Institute ofMetrology, Romania


t e c h n i q u e

Weights: 1 kg 500 g 200 g 200* g 100 g S 100 g

umr hj mg 0.022 0.011 0.0044 0.0044 0.0022 0.0022

Vr hj cm3 127.7398 63.8699 25.5480 25.5480 12.7740 12.7740

uVr hj cm3 0.0012 0.0006 0.0002 0.0002 0.0001 0.0001

Vj cm3 - 62.428 24.975 24.976 12.485 12.506

uVj cm3 - 0.014 0.004 0.004 0.002 0.001

r a mg/cm3 1.196

ur a mg/cm

3 0.002

(VjVr hj)u r a mg - 2.9 10-3 1.15 10-3 1.15 10-3 5.8 10-4 5.4 10-4

(r a r o)(u2Vj+u

2Vr)

1/2 mg - 5.6 10-5 1.61 10-5 1.61 10-5 8 10-6 4.3 10-6

ub mg - 0.003 0.0011 0.0011 0.0006 0.0005

ud mg 0.004

uA mg 0.0035 0.0022 0.0022 0.0022 0.0022

uc mg 0.022 0.0126 0.0064 0.0064 0.0051 0.0051

k 2

U mg 0.04 0.03 0.01 0.01 0.01 0.01

Table 1 Uncertainty budget for the first decade

Introduction

Determining the moisture content of grain andoleaginous foods is just as important as determiningtheir protein content prior to their sale. If the moisturecontent is too high, the grain must first be dried toachieve a moisture content that is low enough for thegrain to be stored - this is a costly and time-consumingprocess. In addition, comminution of grain demands aspecific moisture content and this requirement must becomplied with as closely as possible. The moisturecontent of grain and oleaginous foods thus has aconsiderable influence on the sale price which can beobtained; consequently rapid and exact determination ofthe moisture content during harvesting, storage andprocessing is of utmost economic importance.

In Germany, hygrometers used in official or com-mercial transactions must be verified before they can beused in the field - in fact these instruments must be typeapproved by the Physikalisch-Technische Bundesanstalt(PTB) for the grains and oleaginous foods they areintended to measure.

In accordance with the procedure applied, hygro-meters are classified into measuring instruments used:

to determine the moisture content by drying; and to measure a moisture-dependent physical quantity

such as electrical resistance, capacitance or reflection,or absorption of near infrared radiation.

Measurements whereby the moisture content isdetermined by drying the grain and subsequentlydetermining the loss of mass are generally too expensiveand time-consuming for trade in cereals: results areobtained more rapidly by devices which determine themoisture content by measuring a physical quantity.

Near infrared transmission spectral analyzer

In April 1998, a device which works on a new measuringprinciple was approved in Germany for the measure-ment of the moisture content of wheat, rye, barley andtriticale in the range from 10 % to 20 % (See Fig. 1).Further approvals have been granted in the USA (FGIS),Canada (CGC), Argentina (I.A.S.C.A.U), Denmark (PlantDirectory) and South Africa (Wheat Board).

Description of the measurement principle

The functional principle of an N.I.T. (Near InfraredTransmission) device is depicted in Fig. 2:

- Light from a halogen lamp is directed onto a mono-chromatic mirror.

- This mirror generates monochromatic radiation in thewavelength range between 800 nm and 1100 nm.

- With the aid of an electronic-mechanical control tech-nique, the wavelength range from 850 nm to 1050 nmis applied to the sample at wavelength steps of 2 nm.

- Part of the light is reflected or absorbed by the sample;the other part, the transmitted light, is received by adetector.

The absorption of light varies as a function of thecomposition of the different sample components, suchas moisture, protein, fat and fiber structure, theabsorbance being decisively determined by the layerthickness of the sample. Measuring vessels with a layerthickness of 18 mm are used for wheat, rye, barley andspelt and a measuring cell with variable layer thicknessis used for other grains to be measured. The requiredlayer thickness is set in line with the grains to bemeasured with the help of a servomotor.


e v o l u t i o n s

MOISTURE MEASUREMENT

Near infrared transmittancefor measuring the moisturecontent of grains

KILIAN CONRADI, Verification Board of Rhineland-Palatinate, Germany

Fig. 1 The Foss Infratec 1229 Grain Analyzer

Measurement is started with a scan, without thesample, carried out as a reference measurement over thewhole wavelength range. The detector system thusdetermines the light intensity furnished by the system.Subsequently, after having been filled into the samplefunnel, the sample is automatically transported to themeasuring vessel. In the course of the measurement, theintensities of the 100 selected wavelengths are deter-mined. Then the absorbance values are calculated by thecomputer system. The values obtained furnish a spectro-gram with peaks which are characteristic of the samplemeasured.

From Fig. 3, the moisture and protein values canthen be determined with the aid of a calibrationtranscribed via the network (see below) or copied froma floppy disk.

The calibrations for the individual components aredefined by the instrument manufacturers, in terms ofsuitable laboratory reference procedures, by anadjustment calculus according to the least squaresmethod. The PTB then checks these calibrations and, ifcorrectness has been proved, grants an approval. Fromthe verification law point of view, only the moisturevalue is of significance though various interested partiesalso request a verified determination of the proteincontent. This is why the possibility is being consideredof evaluating the calibrations with respect to the proteincontent within the scope of a special test.

The advantages of the N.I.T. procedure over the othermethods of measurement are the following:

the sample must not be bruised for the analysis; prompt measurement results; the measurement results are independent of sample

temperature and ambient temperature; simultaneous determination of several quality charac-

teristics (e.g. moisture and protein); measuring devices with networking capability.

During a single measurement process the devicecarries out ten individual measurements. The samplequantity (which varies between 300 g and 500 g) is fed to

the device without having been bruised (see Fig. 4). Themeasuring cycle then takes approximately 40 seconds,following which the measurement result is indicated onthe digital display. In addition, the standard deviation ofthe ten individual measurements can be retrieved, whichallows conclusions to be drawn concerning samplehomogeneity.

The NITNET network

The analyzers can be used most efficiently when they areinterconnected by a network. At present, four N.I.T.networks exist in Germany:

Doemens Calibrierdienst (DOEMENS-NITNET) nearMunich;

Raiffeisen HG Nord (RHG-NITNET) in Hanover; Network Rhineland-Palatinate (RLP-NITNET) in

Leideneck; VDLUFA Network (VDLUFA-NITNET) in Kassel.

Approximately 180 N.I.T. analyzers are intercon-nected within these four networks which are inde-pendent of each other. They are connected as satellites totheir network operator in a star pattern via a modemand transcription to, or modification of, the calibrationson the individual devices is possible only via this modemfrom the central processing unit of the networkoperator. This prevents manipulation of the calibrationsby the measuring instrument user.

Verification

In contrast to the laboratory reference procedure andthe electrical hygrometers, the N.I.T. devices determineonly the water fraction which is molecularly bound inthe grain and not the water possibly adherent to the


e v o l u t i o n s

Fig. 2 Functional principle of an N.I.T.

dish. It was, therefore, necessary to open up new pathsfor the verification of these measuring instruments.

Foss submits the calibrations developed to the PTBfor examination and approval. These calibrations aretranscribed to the PTBs master device and checked forcorrectness. After that, the three submasters available atthe verification authorities of Bavaria, Lower Saxonyand Rhineland-Palatinate are compared with the PTBsmaster (see Fig. 5). A maximum deviation of 0.2 % ispermissible. With the aid of these submasters, the usersmeasuring instruments are then verified in accordancewith the approval.

The first verification of grain analyzers in Germanytook place in Rhineland-Palatinate in July 1998. To date,about 80 devices have been verified in Rhineland-Palatinate and if subsequent verifications are includedthe total result is 125 verifications.

Verification test

The verification technological test comprises:

(i) Functional test with granulate

Three measurements are carried out in succession witha granulate specially produced for this purpose. Theindication must lie in the interval 100 0.5. If thiscondition is not complied with, testing of the device isstopped.

(ii) Comparison of the device tested with the submaster

Comparisons between the device tested and the masterare carried out with two samples of each type of grainapproved. Any commercial grain or seed can be used as


e v o l u t i o n s

Fig. 3 Graphical representation of a spectral analysis of wheatwith the following component values:

Moisture: 20.4 %Protein: 14.0 %Spectral measuring range: 850 nm to 1050 nmPoints of measurement: 100 (corresponding to a resolution

of 2 nm)

Fig. 4 Filling of the grain sample to be measured

Fig. 5 Connection of submasters to PTBs master device

sample material. The moisture content of one of thesamples must be between 11 % and 12 %, that of theother between 14 % and 15 %. The grain may also bemoistened; care must, however, be taken that the samplematerial is thoroughly moistened. This can be achievedby ensuring a sufficiently long mixing time (about threedays).

Each sample must be measured three times by thesubmaster and three times by the device tested. Themean values of the measurement results obtained by thesubmaster and the device tested must not deviate bymore than 0.2 %.

A problem encountered upon verification, inparticular on hot days in rooms without air-conditioning, is that samples with higher moisturevalues may dry out during measurement. Practicalapplications have shown that the moisture value maychange by 0.1 % during a test cycle involving a sub-master and the device tested. When several devices areverified it is, therefore, necessary to recheck themoisture value on the master after each measurementcomprising three individual measurements. The timeand effort required for this procedure are such that onlyfour to six devices can be verified each day. Solutions aretherefore being sought which will allow the annualsubsequent verification to be carried out in futuretogether with the network operator in the form of anintercomparison.

It is difficult to furnish reliable figures about meas-urement stability due to the fact that all the deviceswhich were verified were subsequently also calibratedfor various grains - this was carried out just prior to the

subsequent verification. Furthermore the devices will bemaintained and if necessary repaired. Therefore, themeasurement error during verification cannot becompared to the measurement error of moisture deter-mination after the device has been in operation for oneyear. However, the reproducibility with a deviation of 1digit (0.1 %) measurement results is very good.

Summary and conclusions

The new N.I.T. devices offer the possibility to determinethe important quality characteristics of grain andoleaginous foods quickly and without the risk ofoperator errors. Devices operated in a network furnishresults with very small deviations not only for moisturemeasurements, but also for other parameters such asprotein.

Practical application will still have to show to whatextent the correctness is guaranteed, in particular in thecase of grain whose biological characteristics deviatefrom those serving as a standard, where measurementstability is higher compared to hygrometers whichmeasure electrical resistance or capacity.

Furthermore it has been shown that N.I.T. networkinstruments considerably improve relations betweenproducers and traders, since producers are certified andevery trader who is connected to the network can supplyand certify a certain product quality. K


e v o l u t i o n s

KILIAN CONRADI, Verification Board ofRhineland-Palatinate,

Germany

One of Don Boscos most noteworthy pieces of work is ofparticular relevance to the teaching of metrology: Ilsistema metrico decimale ridotto a semplicit precedutodalle quattro operazioni dellaritmetica ad uso degliartigiani e della gente di campagna (literal translation:The decimal metric system reduced to simplicity, pre-ceded by the four arithmetical operations of use to crafts-men and country people), published by Paravia, Turin in1846.

In Italy the decimal units system was introduced atthe same time as a number of other innovations - thisalso happened to be the time when the French armiesheaded by Napoleon Bonaparte invaded the Kingdom ofPiemonte - although discussions on the uniformity ofthe units system as a useful scientific tool had alreadystarted some time before.

In 1793 when the French National Assembly beganstudying a new units system based on the length of theEarth meridian, some Italian States (Granducato diToscana, Repubblica Cisalpina, Repubblica Ligure, Regnodi Sardegna, la Repubblica Piemontese) contributed tothe French project, which is considered to be the mostexcellent example of scientific cooperation over thetimes.

When the French armies arrived in Italy, conqueringits most important nations, they introduced by law themetrication of the units system - thus eliminating deiure the preceding systems.

In Piemonte that happened in 1809, but while themetrication law began to be applied by sending the newunit standards and the related conversion tables to themunicipalities, the Congress of Wien (1814) alsorestored inter alia the old units system all over Europe.

But the charm and the force of the initial idea onwhich the decimal units system was based soon began tobe recognized by intellectuals, although scientificinterests were often mixed in with political motivations.

So, in Piemonte, a Royal Decree was promulgatedwhich provided for the decimal metric system to beadopted as a mandatory units system.

But the promulgation of a new law is not enough tochange long-standing habits based on the use oftraditional weights and measures units and on multiplesand sub-multiples originally determined by means ofcontinuous multiplying and dividing by two.

Disadvantaged people were a major hurdle to thediffusion of the new decimal system because they pre-dominantly continued to use the ancient weights andmeasures in their everyday businesses.

On the other hand, Public State Schools, which wereintroduced in Piemonte in 1822, were not mandatoryand thus not able to help to efficiently spread the wordabout the new system amongst ordinary people.

However Public State Schools did contribute topromoting the new decimal system by means of teach-ing courses - though these courses were of morerelevance to educated people than to the common mortallacking a sound mathematical and scientific back-ground!

The Central Government invited the local authoritiesto do their best to increase the coverage and usage of thenew units system throughout society.

The Roman Church, with its network structure andauthority based on the medieval custom of acquiringand applying knowledge, played a primary role incontributing to spreading the word concerning the newunits system.

Don Boscos work was initiated in a very complexhistorical and social landscape with the clear intentionof encouraging disadvantaged people to use the newdecimal units in their everyday businesses. His book isconceived as a dialog and such a choice was not bychance since he knew, as a well established teacher, thathe would have to use a friendly teaching tone to capturethe masses attention.

The choice of the dialog form for his work wasdetermined as a means to reduce or even eliminate thecultural distance between the writer and disadvantagedreaders, in order to involve them in a knowledge acquisi-tion process as gradually as possible.

Don Bosco dramatized his work by means of atheater play, which was performed in the risingOratories of the Salesian Congregation where the playcombined amusement, reflection and learned instruc-tion.

Don Boscos work was published four years beforethe mandatory introduction of the metric system inPiemonte and even before that, Vicar Apostolic GeneralMons. Filippo Ravina advised parish priests to con-tribute to spread word about the new units system.

The challenge that Don Bosco faced with enthusiasmwas not only a pedagogic one but a social one too: byallowing common people to understand the decimalmetric units system, he raised them to the rank ofcitizens who were able to actively share in the eco-nomic and social life of their community.


e v o l u t i o n s

ITALIAN HISTORY

The decimal units systemand San Giovanni Bosco: A singular meeting betweenscience and pedagogy

SILVANA IOVIENO and LILIANA SMERALDO,Camera di Commercio di Napoli, Italy

Don Boscos work was very successful amongcontemporaries and that is witnessed by the twenty-eight thousand copies and more that were sold, as wellas by the praise of Monsignor Filippo Farina, Bishop ofAsti.

Efforts made by such illustrious men - Don GiovanniBosco and others - should encourage our contempor-aries to reflect on the need to foster and promote themetrology culture in order to equally extend the scopeand application of metrology to non-academic environ-ments. K

Bibliography

K.Kula Le misure e gli uomini dallantichit ad oggiEdizione La TerzaSac...LemoyneMemorie bibliografiche di Don Bosco Vol II S.B.Cavanese 1901S.Scrofani De pesi e delle misure e monete dItalia di SaverioScrofani corrispondente dellIstituto Nazionale di Francia Napoli 1812Tutto Misure Linsegnamento del Sistema metrico decimaleEdizione Mortarino


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SILVANA IOVIENOCamera di Commercio di Napoli, Italy

LILIANA SMERALDO

23

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O I M L B U L L E T I N V O L U M E X L I I N U M B E R 3 J U LY 2 0 0 1

REDUCING TECHNICAL TRADEBARRIERS

Second Triennial Review ofthe WTO Agreement onTechnical Barriers to Trade(TBT) Results and Scope

PROF. HENRI SCHWAMM, Honorary Professor of Economics, University of Geneva

Why was there a need for a Triennial Review of the operation and implementation of the WTO Agreement on Technical Barriers to Trade?

In the first place, such a Review provides answers towhy the Agreement was set up and how it hasfunctioned up to the present time. It offers members ofthe WTO a chance to ask for clarifications on thefunctioning of the Agreement, and also allows them toagree on improvements that should be made to it. It isan opportunity for the active participation of ISO (as anObserver) in the discussions.

Four other Standards Organizations have Observerstatus in the TBT Committee: the IEC (InternationalElectrotechnical Commission); OIML (InternationalOrganization of Legal Metrology); the UN/ECE (UnitedNations Economic Commission for Europe); and theOCED (Organization for Economic Cooperation andDevelopment).

This Review equally allows thought to be given tothe means that may be brought in to facilitate theeffective participation of developing countries in theinternational standardization and conformity assess-ment work.

Results of the Second Triennial Review in Genevawhich ended in late 2000

The role of international standardization

International standards represent a vital element withinthe TBT Agreement and play a major role in itsimplementation.

However - and herein lies a challenge - the TBTAgreement does not provide any precise definition ofwhat a relevant international standard actually is.This omission can be the source of serious confusion intrade exchanges, and so the TBT Committee hastherefore sought to put this right. A broad and thoroughdebate took place in Geneva between the CommitteeMembers and the Observers; below are some of theproblems raised and the solutions offered.

WTO member countries needed to agree on theeconomic circumstances where particular standardscannot be regarded as relevant. Japan, as party to noregional trade agreement, has proposed that inter-national standards under the TBT Agreement must not

This article was first published in the February 2001 edition of theISO BULLETIN and the BIML is grateful to the Editor of the ISOBulletin for kindly granting permission to reprint it.

Introduction to the TBT Agreement

The WTO (World Trade Organization) Agreement onTechnical Barriers to Trade (TBT) - sometimes referred toas the Standards Code - aims to reduce impediments totrade resulting from differences between nationalregulations and standards.

Standards may vary from country to country. Havingtoo many different standards makes life difficult forproducers and exporters. The need for them to complywith different standards often involves significant costs.If the standards are set arbitrarily, they could be usedas an excuse for protectionism. Standards could thenbecome obstacles to trade. In order to prevent toomuch diversity, the TBT Agreement encouragescountries to use international standards where theseare appropriate. It fully recognizes the importantcontribution that international standards and con-formity assessment systems (ensuring that the require-ments of standards are met by given products andservices) can make to improving efficiency of produc-tion and facilitating international trade.

The development of international standards doesindeed reduce potential market access across barriersfor imports on the home market of each WTO membercountry, and reduces the potential barriers to itsexports to third country markets as well. K

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have adverse effects on competition in the relevantmarket such as, for instance, preventing technologicaldevelopment, and should not be given preference overcharacteristics or requirements of specific regions whenthe needs or interests exist in other regions as well.

Japan is also of the opinion that internationalstandards can no longer cope with technologicaldevelopment, thereby lacking universality, and conse-quently relevance, under the TBT Agreement.

Canada and India highlighted the importance of aconsensus-based decision-making process in inter-national standardization bodies. The criteria requiredinclude: a balanced representation of interest cat-egories, broad geographical representation, an appealsmechanism for the impartial handling of any sub-stantial or procedural complaints, and notification ofstandardization activities in suitable media to affordinterested persons or organizations an opportunity formeaningful contributions.

The TBT Committee noted that situations couldarise where no relevant international standards for agiven product existed. Could the concept of equival-ency as proposed by New Zealand be applied as aninterim measure? New Zealand does not see anyconflict between use of equivalency and the develop-ment of international standards. Indeed, the former canbe an important stepping stone towards the latter andhas merit as a means of reducing unnecessary obstaclesto trade. Hong Kong shared this view. The TBT Com-mittee found it useful to further explore the equivalencyof standards as a temporary measure to facilitate tradein the absence of relevant international standards.

The Committee also considered the particular roleof international standards used as a basis for technicalregulations. Assuming that differing internationalstandards covering the same issue exist, they wouldimpose on countries adopting technical regulations achoice between several relevant international standards.The effect of such a choice would in turn createunnecessary regulatory barriers to trade and thusnegatively impact on the objectives of the TBT Agree-ment. When raising this question, the European Union(EU) illustrated the point by the following example. Ifuse of a specific standard within a technical regulationis made mandatory, and country A incorporates oneamong the variety of different international standardsdevoted to the same subject, it is thereby complyingwith the obligation of the TBT Agreement for membercountries to use international standards as a basis fortechnical regulations. If countries B and C adopttechnical regulations covering the same subject but usedifferent international standards as a basis for theirmandatory regulation, they are also observing theAgreement. Nevertheless the market remains frag-mented, as countries A, B and C, although each iscomplying with the Agreement, would require differentstandards as a basis for mandatory regulation. Conse-quently those countries could reject imports of productsmeeting different international standards but coveringthe same issue.

Such a result would certainly not correspond to thespirit and purpose of the TBT Agreement, the objectiveof which is to facilitate trade and to reduce marketfragmentation, among others, by means of the use of

In the wake of the GATT

The provisions of the GATT 1947 contained only ageneral reference to technical regulations and stand-ards. A GATT working group, set up to evaluate theimpact of non-tariff barriers in international trade,concluded that technical barriers were the largestcategory of non-tariff measures faced by importers.

After years of negotiations at the end of the TokyoRound in 1979, 32 GATT Contracting Parties signedthe pluriannual Agreement on Technical Barriers toTrade (TBT) which laid down the rules for preparation,adoption and application of technical regulations,standards and conformity assessment procedures.

The new WTO Agreement on Technical Barriers toTrade, or TBT Agreement, negotiated during theUruguay Round, strengthens and clarifies theprovisions of the Tokyo Round Standards Code. Itclearly distinguishes between technical regulations andstandards.

The difference between a standard and a technicalregulation lies in compliance. While conformity withstandards is voluntary, technical regulations are bynature mandatory. They have different implications forinternational trade. If an imported product does notfulfill the requirements of a technical regulation, it willnot be allowed to be put on sale. In the case ofstandards, non-complying imported products will beallowed on the market, but then their market share maybe affected if consumers prefer products that meet localstandards.

Conformity assessment procedures are defined by theTBT Agreement as technical procedures - such astesting, verification, inspection and certification - whichconfirm that products fulfill the requirements laid downin regulations and standards. Generally, exportersbear the cost of these procedures. Non-transparent anddiscriminatory conformity assessment procedures canbecome effective protectionist tools. K

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country or region. Consensus procedures should beestablished that seek to take into account the views ofall parties concerned and to reconcile any conflictingarguments.

Impartiality includes: access to participation in work,submission of comments on drafts, consideration ofviews expressed and comments made, decision-making through consensus, obtaining of informationand documents, dissemination of the internationalstandards, fees charged for documents, right totranspose the international standards into regional ornational standards, revision of the internationalstandards.

Effectiveness and relevance. To facilitate interna-tional trade and prevent unnecessary trade barriers,international standards need to be relevant andeffectively respond to regulatory and market needs, aswell as scientific and technological developments invarious countries. They should not distort the globalmarket, have adverse effects on fair competition, orstifle innovation and technological development. Inaddition, they should not give preference to thecharacteristics or requirements of specific countrieswhen different needs and interests exist in othercountries or regions. Whenever possible, internationalstandards should be performance-based rather thanbased on design or descriptive characteristics.

Coherence. In order to avoid the development ofconflicting international standards, it is importantthat international standardizing bodies avoidduplication of, or overlapping with, the work of otherinternational standardizing bodies. In this respect,cooperation and coordination with other relevantstandardization bodies is essential.

Development dimension. Constraints on developingcountries, in particular, to effectively participate instandards development should be taken into con-sideration in the standards development process.Tangible ways of facilitating developing countriesparticipation in international standards developmentshould be sought. Developing countries should not beexcluded de facto from the process. Provisions forcapacity building and technical assistance withinstandardizing bodies are important in this context.

According to the TBT Committee, these principlesand procedures should also be observed when guidesand recommendations are elaborated. ISO confirmedthat they are observed in the preparation process of theCASCO guides.

The Committee agreed that regular information-exchange with relevant bodies involved in the develop-ment of international standards was useful and shouldbe reinforced.

international standards. It is the EUs understandingthat for achieving this purpose such standards shouldbe coherent. The EU therefore supports the ISO/IECprocedures the aim of which is to avoid the coexistenceof conflicting standards. The EU also supports theprinciple of singularity proposed by Brazil, accordingto which for each area of standardization no more thanone international standardizing body should be active.This body should produce a single and coherent set ofinternational standards. International standardizingbodies should act jointly or in cooperation in cases ofoverlapping when their areas of activity converge, be itfor scientific, technological or regulatory reasons. Thisis also Mexicos point of view: in the case of two inter-national standardizing bodies working in the samearea, a coordination mechanism should be put in placeso as to avoid duplication.

ISO gave its assurance that it would report to theTBT Committee on action taken to avoid duplicationand ensure consistency between international stand-ards. ISO also promised to report on its activities toaddress the specific needs of developing countries.

Taking these suggestions fully into account, and inorder to clarify and to strengthen the concept ofinternational standards under the Agreement and tocontribute to the advancement of its objectives, theTBT Committee adopted a list of six principles thatshould be observed by international standardizingbodies: transparency, openness, impartiality, and con-sensus, effectiveness and relevance, coherence, develop-ment dimension.

Transparency. All essential information on currentwork programmes, as well as on proposals forstandards under consideration and on the finalresults should be made accessible to all interestedparties in all WTO member countries.

Openness. Membership of an international standard-izing body should be open on a non-discriminatorybasis to relevant bodies of all WTO membercountries. This would include openness with respectto participation at the policy development level and atevery stage of standards development, such as:proposal and acceptance of new work items, tech-nical discussions on proposals, submission ofcomments on drafts, reviewing existing standards,voting and adoption of standards and disseminationof adopted standards.

Impartiality and consensus. All relevant bodies ofWTO member countries should be provided withmeaningful opportunities to contribute to thedevelopment of an international standard so that thestandard development process will neither privilegenor favour the interests of a particular supplier,

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The Committee is perfectly aware of the fact thatinternational standardization is an area in whichdeveloping country participation is still limited andconstrained. Some of the reasons identified for thissituation are the lack of technical capacity, the locationof technical secretariats and technical meetings, thetranslation of international standards into nationallanguages, as well as other constraints in the areas offinancial and human resources which handicapparticipation in meetings. To assist in resolving thisproblem, the Committee noted that it was important toprioritize the international standardization activitiesrelated to products of particular interest to developingcountries. It is also critical for those countries to assessproducts/sectors of priority interest to them for inter-national standardization, so that resources can beappropriately targeted. Another solution is to facilitateeffective participation by means of informationtechnologies, such as using e-mail and video-conferencing as alternatives to traditional meetings.Switzerland expressed its hope that the Committeewould develop a demand-driven technical cooperationprogramme related to the TBT Agreement.

Conformity assessment procedures

The goal of conformity assessment is to ensure that therequirements of standards and technical regulations aremet by given products and services. This is critical inorder for buyers of those goods and services to haveconfidence that legitimate regulatory objectives are metand that the goods and services meet their health, safetyand other needs. Undoubtedly, confidence in theconformity assessment practices and procedures ofother countries is also important to the facilitation oftrade.

Indeed, there is broad support from both developedand developing countries for working towards the goalthrough the principle of one standard, one test, andif required, one certification, one time, as stated inthe First Triennial Review of the TBT Agreement.

Where debate continues, however, is as to thedifferent methods of pursuing the principle. Differentmechanisms exist to facilitate acceptance of results ofconformity assessments: mutual recognition agree-ments (MRAs), voluntary cooperative agreementsbetween domestic and foreign conformity assessmentbodies, government designation, unilateral recognitionof results of foreign conformity assessment, manu-facturers/suppliers declarations.

Japan thinks that the three principles of thestandards development process (transparency, open-

ness and impartiality) should apply equally to thedevelopment process of conformity assessment guidesand recommendations (such as CASCO Guides andstandards) and documents developed by internationaland regional systems for conformity assessment (suchas IAF - International Accreditation Forum - Guidelinesfor CASCO documents).

A new development, encouraged by the TBT Agree-ment, is the conclusion of MRAs on the results ofconformity assessment procedures, concluded betweencountries having established confidence in each otherstesting bodies and procedures. The trend to concludesuch MRAs is confined - to date - to the developedcountries. For example, the European Union hasconcluded MRAs for the results of conformity assess-ment with Australia, Canada, New Zealand, Switzerlandand the United States. Plurilateral MRAs seem to bemore cost-effective than bilateral ones.

Accreditation, that is based on internationalstandards and Guides, represents an independent testof the technical competence of conformity assessmentbodies. Broad global acceptance of accreditation, whichaddresses both regulatory requirements and marketneeds, has provided the basis for the emergence of anumber of international and regional examples ofaccreditation agreements. Further work is needed toencourage greater acceptance of these agreements,particularly among regulators and the public, andstronger participation from developing countries intheir development.

The examination of other less formal approaches toconformity assessment, including suppliers declara-tion of conformity, could be encouraged in order todetermine the costs and benefits and which industrialsectors would most benefit. The supplier may be amanufacturer, distributor, importer, assembler orservice organization. The TBT Committee noted abroad support for the suppliers declaration procedureas specified in ISO/IEC Guide 22.

Private multilateral agreements between certifica-tion organizations, such as the successful IEC systemfor Conformity Testing and Certification of ElectricalEquipment (IECEE CB Scheme) should also be studiedto assess applicability to other sectors.

Chile stated that conformity assessment was themost serious problem for developing countries, requir-ing further concrete steps to be taken by the Commit-tee. Developing country exporters, in particular SMEs,in some cases find themselves faced with conformityassessment requirements in export markets that aredifficult to meet. According to the Committee, this canbe due to the limited physical and technical resourcesfor national conformity assessment, insufficient num-bers of accredited laboratories at the national or

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g) assess the respective advantages of bilateral asagainst multilateral approaches, unisectoral asagainst multisectoral.

Overall assessment of the Second Triennial Review

The Second Triennial Review of the TBT Agreement hasallowed substantial progress to be achieved in the rightdirection. Most members of the Committee welcomedits balanced and forward-looking outcome, whichrepresents a good basis for future discussions. Every-body highlighted the importance of having setguidelines to be used by international standardsorganizations for standards development. While theseguidelines are viewed as a good achievement, it remainsto be seen how they will work in practice. For theUnited States, these principles can at any rate be usedin the future to evaluate adverse trade implications ifand when they arise.

ISO welcomes the fact that the TBT Committeewishes to strengthen the cooperation between theinternational standardizing bodies and its govern-mental delegations. For strengthened cooperation goeshand in hand with greater mutual trust.

The unanimous agreement on the positive spirit andoutcome of this Second Triennial Review augurs wellfor the future because it represents, for developing aswell as for developed countries, a better functioningand better balanced tool for trade facilitation in theinterest of the international trading community as awhole. K

regional level, high costs as well as legal difficulties inobtaining foreign accreditation, difficulties in establish-ing internationally recognized accreditation bodies,difficulties in participating in international conformityassessment systems, as well as difficulties related to theimplementation of ISO/IEC Guides on conformityassessment procedures.

Canada is promoting a common global approachto conformity assessment and believes that ISO/IECGuide 60 (Code of Good Practice for conformity assess-ment), which is designed to promote equal right ofaccess to conformity assessment worldwide, provides agood framework for the performance of all conformityassessment bodies whether governmental or nongovernmental, domestic or international. However, thisGuide is not widely used and needs to be reviewed andupdated, if necessary, to better meet the objectives ofthe TBT Agreement. In the meantime, the ISO Commit-tee on Conformity Assessment (CASCO) has decided toundertake the necessary work.

Before making a final decision on the best way toproceed, WTO negotiators must at all costs keep anumber of key questions in mind:

a) determine the costs versus advantages of the variousapproaches;

b) eliminate any duplication of trial prescriptions;c) foresee the same procedures for local, national and

regional or international bodies whether govern-mental or non governmental;

d) reduce the charges weighing on industry andregulation bodies;

e) take into account the needs of consumers;f) favour non-discriminatory and transparent ap-

proaches that facilitate exchanges; and

More information on the TBT Agreement can be found on the following web site:

http://www.wto.org/wto/english/tratop_e/tbt_e/tbt_e.htm

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E Issuing Authority / Autorit de dlivrance

Physikalisch-Technische Bundesanstalt (PTB),Germany

R61/1996 - NL - 00.01Type MP ... (Class X(1))

Atoma GmbH, Traunreuter Strae 2-4, D-84478 Waldkraiburg, Germany

This list is classified by IssuingAuthority; updated informationon these Authorities may beobtained from the BIML.

Cette liste est classe par Autoritde dlivrance; les informations jour relatives ces Autorits sontdisponibles auprs du BIML.

OIML Recommendation ap-plicable within the System /Year of publication

Recommandation OIML ap-plicable dans le cadre duSystme / Anne d'dition

Certified pattern(s)

Modle(s) certifi(s)

Applicant

Demandeur

The code (ISO) of theMember State in which thecertificate was issued.

Le code (ISO) indicatif del'tat Membre ayant dlivrle certificat.

For each Member State,certificates are numbered inthe order of their issue(renumbered annually).

Pour chaque tat Membre, lescertificats sont numrots parordre de dlivrance (cettenumrotation est annuelle).

Year of issue

Anne de dlivrance

The OIML Certificate System for Measuring Instruments was introducedin 1991 to facilitate administrative procedures and lower costsassociated with the international trade of measuring instruments subjectto legal requirements.

The System provides the possibility for a manufacturer to obtain an OIMLcertificate and a test report indicating that a given instrument patterncomplies with the requirements of relevant OIML InternationalRecommendations.

Certificates are delivered by OIML Member States that have establishedone or several Issuing Authorities responsible for processing applicationsby manufacturers wishing to have their instrument patterns certified.

OIML certificates are accepted by national metrology services on avoluntary basis, and as the climate for mutual confidence and recognitionof test results develops between OIML Members, the OIML CertificateSystem serves to simplify the pattern approval process for manufacturersand metrology authorities by eliminating costly duplication of applicationand test procedures. K

Le Systme de Certificats OIML pour les Instruments de Mesure a tintroduit en 1991 afin de faciliter les procdures administratives etdabaisser les cots lis au commerce international des instruments demesure soumis aux exigences lgales.

Le Systme permet un constructeur dobtenir un certificat OIML et unrapport dessai indiquant quun modle dinstrument satisfait auxexigences des Recommandations OIML applicables.

Les certificats sont dlivrs par les tats Membres de lOIML, qui ont tabliune ou plusieurs autorits de dlivrance responsables du traitement des

demandes prsentes par des constructeurs souhaitant voir certifier leursmodles dinstruments.

Les services nationaux de mtrologie lgale peuvent accepter les certificatssur une base volontaire; avec le dveloppement entre Membres OIML dunclimat de confiance mutuelle et de reconnaissance des rsultats dessais, leSystme simplifie les processus dapprobation de modle pour lesconstructeurs et les autorits mtrologiques par llimination desrptitions coteuses dans les procdures de demande et dessai. K

Systme de Certificats OIML:Certificats enregistrs 2001.022001.04Pour des informations jour: www.oiml.org

OIML Certificate System:Certificates registered 2001.022001.04For up to date information: www.oiml.org

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National Weights and Measures Laboratory (NWML),United Kingdom

R51/1996-GB1-01.01Type 8060 (Classes X(1) and Y(a))

Pelcombe Ltd, Main Road, Dovercourt, Harwich, Essex CO12 4LP, United Kingdom


OIML Chinese Secretariat, St6ate Bureau of Technical Supervision, China

R60/2000-CN-00.01Type CZL-3 (Class C)

Zhongyuan Electrical Measuring Instruments Co., P.O. Box 2, Hanzhong 723007, Shanxi, China

R60/2000-CN-00.02Type CZL-8C (Class C)


R60/2000-CN-00.03Type CZL-6G (Class C)


R60/2000-CN-00.04Type CZL-6E (Class C)


R60/2000-CN-00.05Type CZL-6D (Class C)




R60/2000-DE-01.01Type C16 i (Class D1 up to C4)

Hottinger Baldwin Messtechnic Wgetechnik GmbH,Im Tiefen See 45, D-64293 Darmstadt, Germany

R60/2000-DE-01.02Type PW2 (Classes D1, C3, C3MR and C3MI)

Hottinger Baldwin Messtechnic Wgetechnik GmbH,Im Tiefen See 45, D-64293 Darmstadt, Germany

R60/2000-DE-01.03Type RTN .. (Class C3 to C5)

Schenk Process GmbH, Landwehrstrae 55, D-64293 Darmstadt, Germany

E Issuing Authority / Autorit de dlivranceDanish Agency for Development of Trade and Industry, Division of Metrology, Denmark

R60/2000-DK-01.01Compression, strain gauge load cell, type SC (Class C)

Esit Elektronik Sistemler Imalat ve Ticaret Ltd. STI,Mhrdar Cad. 91 Kadiky, TR-81300 Istanbul, Turkey

R60/2000-DK-01.02Shear beam, strain gauge load cell, type SBS (Class C)


R60/2000-DK-01.03Single point, strain gauge load cell, type SP (Class C)


INSTRUMENT CATEGORYCATGORIE DINSTRUMENT

Automatic catchweighing instrumentsInstruments de pesage trieurs-tiqueteurs fonctionnement automatique

R 51 (1996)


Metrological regulation for load cells(applicable to analog and/or digital load cells)Rglementation mtrologique des cellules de pese(applicable aux cellules de pese affichageanalogique et/ou numrique)

R 60 (2000)

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Laboratoire National dEssaisService Certification et Conformit TechniqueCertification Instruments de Mesure, France

R60/2000-FR2-00.01SCAIME bending beam load cell with strain gauges,Types APC.SH5e, APC.SH10e, APC.SH15e(Accuracy class C)

Scaime S.A., Z.I. de Juvigny, B.P. 501, F-74105 Annemasse cedex, France


Netherlands Measurement Institute (NMi) Certin B.V.,The Netherlands

R60/2000-NL1-01.01Type LBD1 (Class C)

Charder Electronic Co., Ltd, 103, Kuo Chung Road,Dah Li City, Taichung Hsien 412, R.O.C., Taiwan

R60/2000-NL1-01.02Type 1130 (Class C)

Tedea Huntleigh International Ltd., 5a Hatzoran St.,Netanya 42506, Isral

R60/2000-NL1-01.03Type 0795 (Class C)

Mettler-Toledo Inc., 1150 Dearborn Drive, Worthington,Ohio 43085-6712, USA

R60/2000-NL1-01.04Type GD or 0782 (Class C)

Mettler-Toledo Changzhou Scale Ltd., 111 Changxi Road, Changzhou, Jiangsu 213001, China

R60/2000-NL1-01.05Type CPI (Class C)

Precia S.A., BP 106, F-07001 Privas cedex, France

R60/2000-NL1-01.06Type 0785 (Class C)

Mettler-Toledo Inc., 150 Accurate Way, Inman, SC 29349, USA

R60/2000-NL1-01.07Type MED-400 (Class C)

HBM Inc., 19 Bartlett Street, Marlboro, MA 01752, USA

R60/2000-NL1-01.08 Rev. 1Type CA40X (Class C)

Scaime S.A., Z.I. de Juvigny, B.P. 501, F-74105 Annemasse cedex, France

R60/2000-NL1-01.09Type 1130 (Class C)

Tedea Huntleigh International Ltd., 5a Hatzoran St.,Netanya 42506, Isral

R60/2000-NL1-01.10Type BCS (Class C)

CAS Corporation, CAS Factory # 19 Kanap-ri,Kwangjeok-myon, Yangju-kun Kyungki-do, Rep. of Korea



R61/1996-NL1-01.01Types CCW-M-****(*)-*/**-**, CCW-EM-****(*)-*/**-**,CCW-NZ-****(*)-*/**-**, CCW-RZ-****-*/**-**-N, CCW-DZ-****-*/**-**-N (Class X(1))

Ishida Co., Ltd., 44, Sanno-cho, Shogoin, Sakayo-ku,Kyoto-city 606-8392, Japan

R61/1996-NL1-01.02Type WT-WMA-2 (Class Ref(1))

Wet B.V., Minervum 1719, 4817 ZK Breda, The Netherlands

R61/1996-NL1-01.03Type Duplex Weighmaster (Class X(1))

Thiele Technologies Inc., 315, 27th Avenue Northeast,Minneapolis, Minnesota 55418-2715, USA

R61/1996-NL1-01.04Model TW-.... (Class X(1))

Neupak, 3680-1 Dodd Road, St. Paul, MN 55122, USA


Automatic gravimetric filling instrumentsDoseuses pondrales fonctionnement automatique

R 61 (1996)

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u p d a t e




R76/1992-DE-00.09 Rev. 1Type iso-TEST (Classes I, II, III and IIII)

Sartorius A.G., Weender Landstrae 94-108, D-37075 Gttingen, Germany

E Issuing Authority / Autorit de dlivranceDanish Agency for Development of Trade and Industry, Division of Metrology, Denmark

R76/1992-DK-01.01Type M1100-Cx (Classes III and IIII)

Marel hf, Hofdabakka 9, IS-112 Reykjavik, Iceland



R76/1992-NL1-01.04Type 8217 (Class III)

Mettler-Toledo Inc., 1150 Dearborn Drive, Worthington, Ohio 43085-6712, USA

R76/1992-NL1-01.05Type SC600 (Class III)

Shekel Electronics Scales, Kibbutz Beit Keshet, M.P. Lower Galilee 15247, Isral

R76/1992-NL1-01.06Type DT-15 (Class III)

DATECS Ltd.A, 125, Tsarigrag shosse, bl 26B, Sofia 1113, Bulgaria

R76/1992-NL1-01.07Type IWQ-series (Class III)

Ishida Co., Ltd., 44, Sanno-cho, Shogoin, Sakayo-ku,Kyoto-city 606-8392, Japan

R76/1992-NL1-01.08Types AB-S, GB-S and PB-S (Classes I, II and III)

Mettler-Toledo A.G., Im Langacher, CH-8606 Greifensee, Switzerland

R76/1992-NL1-01.09Type BM-3 (Class III)

Digital Scales S.A., Poligono Industrial Larrondo,Beheko Etorbidea, no. 2 Naves 2, 3, 4, 48180 Loiu Vizcaya, Spain


Gosstandart of Russian Federation, Russian Federation

R76/1992-RU-00.03Scale SHTRIKH M (Class III)

SHTRIKH-M, 1, Kholodilny pereulok, Moscow, 113191,Russian Federation

E Issuing Authority / Autorit de

Oiml Bulletin July 2001

Documents

Transcript of Oiml Bulletin July 2001