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Guide 98-1
Second edition
Guide to the expression of
2024-02
uncertainty in measurement —
Part 1:
Introduction
Guide pour l'expression de l'incertitude de mesure —
Partie 1: Introduction
Reference number
© ISO/IEC 2024
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— most conceptual and technical aspects have been removed.
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iii
Joint Committee for Guides in Metrology
Guide to the expression of uncertainty in measurement
— Part 1: Introduction
Guide pour l’expression de l’incertitude de mesure — Partie 1:
Introduction
JCGM GUM-1:2023
© JCGM 2023 – All rights reserved
© ISO/IEC 2024 – All rights reserved
ii JCGM GUM-1:2023
© JCGM 2023
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JCGM GUM-1:2023 iii
Contents
Page
Foreword iv
1 Scope 1
2 Rationale 1
3 Measurement 2
4 Guidance on evaluating measurement uncertainty 3
5 Parts of the GUM 5
5.1 Using the law of propagation of uncertainty (JCGM 100:2008) . . . . . . . . . . . . . 5
5.2 Conformity assessment (JCGM 106:2012) . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3 Measurement models (JCGM GUM-6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.4 Propagation of distributions (JCGM 101:2008) . . . . . . . . . . . . . . . . . . . . . . . 7
5.5 Extension to any number of output quantities (JCGM 102:2011) . . . . . . . . . . . . 8
Annexes 9
A Overview of the parts of the GUM 9
References 10
© JCGM 2023 – All rights reserved
© ISO/IEC 2024 – All rights reserved
iv JCGM GUM-1:2023
Foreword
In 1997 a Joint Committee for Guides in Metrology (JCGM), chaired by the Director of the
Bureau International des Poids et Mesures (BIPM), was created by the seven international
organizations that had originally in 1993 prepared the ‘Guide to the expression of uncer-
tainty in measurement’ and the ‘International vocabulary of basic and general terms in
metrology’. The JCGM assumed responsibility for these two documents from the Technical
Advisory Group 4 of the International Organization for Standardization (ISO/TAG4).
The Joint Committee is formed by the BIPM with the International Electrotechnical Com-
mission (IEC), the International Federation of Clinical Chemistry and Laboratory Medicine
(IFCC), the International Laboratory Accreditation Cooperation (ILAC), the International
Organization for Standardization (ISO), the International Union of Pure and Applied Chem-
istry (IUPAC), the International Union of Pure and Applied Physics (IUPAP) and the Inter-
national Organization of Legal Metrology (OIML).
JCGM has two Working Groups. Working Group 1, ‘Expression of uncertainty in mea-
surement’, has the task to promote the use of the ‘Guide to the expression of uncertainty
in measurement’ and to prepare documents for its broad application. Working Group 2,
‘Working Group on International vocabulary of basic and general terms in metrology’, has
the task to revise and promote the use of the ‘International vocabulary of basic and general
terms in metrology’ (the ‘VIM’).
In 2008 the JCGM made available a slightly revised version (mainly correcting minor er-
rors) of the ‘Guide to the expression of uncertainty in measurement’, labelling the docu-
ment ‘JCGM 100:2008’.
In 2017 the JCGM rebranded the documents in its portfolio that have been produced by
Working Group 1 or are to be developed by that Group. The whole suite of documents is
now known as the ‘Guide to the expression of uncertainty in measurement’ or ‘GUM’, and
is concerned with the evaluation and expression of measurement uncertainty, as well as
its application in science, trade, health, safety and other societal activities.
This part of the suite introduces the processes involved and the subsequent parts in this
suite giving specific guidance on these processes. This document replaces JCGM 104:2009.
This document has been prepared by Working Group 1 of the JCGM, and has benefited
from detailed reviews undertaken by member organizations of the JCGM and National
Metrology Institutes.
© JCGM 2023 – All rights reserved
© ISO/IEC 2024 – All rights reserved
JCGM GUM-1:2023 1
Guide to the expression of uncertainty in
measurement — Part 1: Introduction
1 Scope
The ‘Guide to the expression of uncertainty in measurement’ (GUM) establishes general
rules for evaluating and expressing uncertainty in measurement from the shop floor to
fundamental research. Therefore, the principles of this suite of documents are intended to
be applicable to a broad spectrum of measurements and their applications. An overview
of the parts of the GUM is given in table A.1 in Annex A.
NOTE Where the acronym GUM is used in this document, it refers to the suite of documents. An
individual part of the GUM is referred to by its corresponding JCGM numbering (e.g., part 6 of the
GUM is JCGM GUM-6:2020).
This document gives a rationale for evaluating, expressing and using measurement un-
certainty (Clause 2). A brief introduction is given to measurement (Clause 3) and to the
decisions involved when evaluating measurement uncertainty (Clause 4). In Clause 5, a
brief description of the contents of the parts of the GUM is given. In each of these clauses,
the relevant parts of the GUM are identified for further guidance.
2 Rationale
2.1 Measurement [12, Definition 2.1] is one of the most common processes in human
activity. Measured values of quantities [12, Definition 2.10] are required for a diverse
range of applications and, for each of these values, a statement is needed about its credi-
bility. Such a statement is usually expressed in terms of measurement uncertainty[12, Def-
inition 2.26]. The two components, the measured value and the associated uncertainty,
together constitute the most common way of reporting a measurement result[12, Defini-
tion 2.9]. In cases where values for more than one quantity are provided by the measure-
ment, a more elaborate statement of the uncertainty is often required (Clause 5.5; see also
Clause 3.1).
2.2 Measurements are performed in many branches of society for widely different pur-
poses. Many measurements performed on a daily basis, often in automated processes,
concern trade and commerce. Reliable measurement results are also needed for mak-
ing informed decisions in for example health, safety, weather forecasts, law enforcement
and science. Measurements are performed by for example greengrocers, technicians, en-
gineers, laboratory staff, health care professionals, scientists and individuals at home, in
very different contexts.
2.3 Many measurements are made for the purpose of comparison of results with speci-
fications. Such a comparison can be made for widely different purposes. This activity is
generally known as conformity assessment [3, Definition 4.1] [10, Definition 3.3.1]; see
also Clause 5.2.
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© ISO/IEC 2024 – All rights reserved
2 JCGM GUM-1:2023
2.4 Comparison of measurement results is
...