ISO/TR 16476:2016

TECHNICAL ISO/TR
REPORT 16476
First edition
2016-06-01
Reference materials — Establishing
and expressing metrological
traceability of quantity values
assigned to reference materials
Matériaux de référence — Etablissement et expression de la
traçabilité métrologique de valeurs assignées à des matériaux de
référence
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 The VIM definition of metrological traceability . 1
3 Challenges arising from the definition of metrological traceability .2
3.1 Conventions . 2
3.2 (C)RM as the carrier of traceable values. 3
3.3 Implicit traceability to the unit of the measurement scale . 4
3.4 Traceability networks . 5
3.5 Properties expressed in units of measurement scales other than the SI . 5
3.6 Properties other than quantitative . 6
3.7 Summary of an ISO/REMCO event on metrological traceability . 6
4 Approaches to metrological traceability of (C)RM . 7
4.1 General . 7
4.2 Approach A . 7
4.3 Approach B . 8
5 Establishing traceability of (C)RM property values (Approach B) . 9
5.1 Principles . 9
5.2 Traceability pathways .10
5.3 Steps in establishing traceability .10
5.3.1 General.10
5.3.2 Combining results .11
5.4 Summary .12
6 Reporting traceability .12
6.1 Inquiry .12
6.2 Results of the inquiry .12
6.3 Requirements .13
6.4 Formats .14
6.5 Further recommendations .16
Annex A (informative) Worked-out example .17
Annex B (informative) Catalogue of analytes and measurement areas covered by WHO .19
Annex C (informative) Example for method-independent, SI traceable values obtained by
inter-laboratory comparison .21
Bibliography .22
Foreword
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ISO/TR 16476 was prepared by the ISO Committee on Reference Materials (ISO/REMCO).
iv © ISO 2016 – All rights reserved

Introduction
Reference materials (RM), in particular when certified (CRM), are a major tool for assuring the quality
and reliability of results obtained in measurement and testing. CRM property values, in particular used
for assessing the trueness of a measurement procedure as implemented in a laboratory, also establish
traceability of the measurement result. Which reference the property values assigned to (C)RM should
be traceable to, and how this traceability should be established, demonstrated, and reported on
certificates is, therefore, a question of primary importance, mainly for RM producers. However, users of
(C)RMs should also know what the endpoint of their traceability chain is, in particular for all purposes
of cross-border acceptance of measurement results.
It was therefore considered necessary to conduct a study into existing principles for, and requirements
to, the traceability of (C)RM, in particular with a specific view to the current definition of metrological
traceability given by the Vocabulary of International Metrology (VIM), edition 3, 2007.
TECHNICAL REPORT ISO/TR 16476:2016(E)
Reference materials — Establishing and expressing
metrological traceability of quantity values assigned to
reference materials
1 Scope
This Technical Report investigates, discusses, and specifies further, the general principles of establishing
traceability of measurement results laid down in the Joint BIPM, OIML, ILAC and ISO Declaration on
[1]
Metrological Traceability , in particular for values assigned to (certified) reference materials. The
document covers the following topics:
a) a study into existing principles for, and requirements to, the traceability of the value assigned to the
property of a (C)RM, with a specific view to the current definition of metrological traceability given
[2] [21]
by the 2007 edition of the VIM (published also as JCGM 200:2008 and ISO/IEC Guide 99:2007 );
b) the development of a sensible, widely applicable approach to the understanding of the traceability
of a value assigned to (C)RM property;
c) recommendations on how traceability should be established, demonstrated, and reported on
certificates and other documents accompanying (C)RM.
The developed approach is exemplified for measurement procedures not covered earlier by other
guidance documents on the topic.
2 The VIM definition of metrological traceability
[2],[21]
The recent edition of the VIM defines metrological traceability (term 2.41) as
property of a measurement result whereby the result can be related to a reference through a documented
unbroken chain of calibrations, each contributing to the measurement uncertainty
NOTE 1 For this definition, a ‘reference’ can be a definition of a measurement unit through its
practical realization, or a measurement procedure including the measurement unit for a
non-ordinal quantity, or a measurement standard.
NOTE 2 Metrological traceability requires an established calibration hierarchy.
NOTE 3 Specification of the reference must include the time at which this reference was used in
establishing the calibration hierarchy, along with any other relevant metrological infor-
mation about the reference, such as when the first calibration in the calibration hierarchy
was performed.
NOTE 4 For measurements with more than one input quantity in the measurement model, each
of the input quantity values should itself be metrologically traceable and the calibration
hierarchy involved may form a branched structure or a network. The effort involved in
establishing metrological traceability for each input quantity value should be commensu-
rate with its relative contribution to the measurement result.
NOTE 5 Metrological traceability of a measurement result does not ensure that the measurement
uncertainty is adequate for a given purpose or that there is an absence of mistakes.
NOTE 6 A comparison between two measurement standards may be viewed as a calibration if the
comparison is used to check and, if necessary, correct the quantity value and measure-
ment uncertainty attributed to one of the measurement standards.
NOTE 7 The ILAC considers the elements for confirming metrological traceability to be an un-
broken metrological traceability chain to an international measurement standard or a
national measurement standard, a documented measurement uncertainty, a documented
measurement procedure, accredited technical competence, metrological traceability to
the SI, and calibration intervals (see ILAC P-10:2002).
NOTE 8 The abbreviated term “traceability” is sometimes used to mean ‘metrological traceabil-
ity’ as well as other concepts, such as ‘sample traceability’ or ‘document traceability’ or
‘instrument traceability’ or ‘material traceability’, where the history (“trace”) of an item
is meant. Therefore, the full term of “metrological traceability” is preferred if there is any
risk of confusion.
NOTE 7 makes clear that the measurement method/procedure is a part of the traceability statement,
but insufficient if taken alone. This implies that a measurement resu
...