International

 

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ISO/IEC 17025:2017(E)

Annex A 

(informative) 

 

Metrological traceability

A.1 General

This annex provides additional information on metrological traceability, which is an important concept 

to ensure comparability of measurement results both nationally and internationally.

A.2  Establishing metrological traceability

A.2.1  Metrological traceability is established by considering, and then ensuring, the following:

a)  the specification of the measurand (quantity to be measured);

b)  a documented unbroken chain of calibrations going back to stated and appropriate references 

(appropriate references include national or international standards, and intrinsic standards);

c)  that  measurement  uncertainty  for  each  step  in  the  traceability  chain  is  evaluated  according  to 

agreed methods;

d)  that each step of the chain is performed in accordance with appropriate methods, with the 

measurement results and with associated, recorded measurement uncertainties;

e)  that the laboratories performing one or more steps in the chain supply evidence for their technical 

competence.

A.2.2  The  systematic  measurement  error  (sometimes  called  “bias”)  of  the  calibrated  equipment  is 

taken into account to disseminate metrological traceability to measurement results in the laboratory. 

There are several mechanisms available to take into account the systematic measurement errors in the 

dissemination of measurement metrological traceability.

A.2.3  Measurement  standards  that  have  reported  information  from  a  competent  laboratory  that 

includes  only  a  statement  of  conformity  to  a  specification  (omitting  the  measurement  results  and 

associated uncertainties) are sometimes used to disseminate metrological traceability. This approach, in 

which the specification limits are imported as the source of uncertainty, is dependent upon:

—  the use of an appropriate decision rule to establish conformity;

—  the  specification  limits  subsequently  being  treated  in  a  technically  appropriate  way  in  the 

uncertainty budget.

The technical basis for this approach is that the declared conformance to a specification defines a range 

of measurement values, within which the true value is expected to lie, at a specified level of confidence, 

which considers both any bias from the true value, as well as the measurement uncertainty.

EXAMPLE 

The use of OIML R 111 class weights to calibrate a balance.