1.1 This Guide establishes general rules for evaluating and expressing uncertainty in measurement that
can be followed at various levels of accuracy and in many fields — from the shop floor to fundamental
research. Therefore, the principles of this Guide are intended to be applicable to a broad spectrum of
measurements, including those required for:
-maintaining quality control and quality assurance in production;
-complying with and enforcing laws and regulations;
-conducting basic research, and applied research and development, in science and engineering;
-calibrating standards and instruments and performing tests throughout a national measurement system in
order to achieve traceability to national standards;
-developing, maintaining, and comparing international and national physical reference standards, including
reference materials.
1.2 This Guide is primarily concerned with the expression of uncertainty in the measurement of a
well-defined physical quantity — the measurand — that can be characterized by an essentially unique value. If
the phenomenon of interest can be represented only as a distribution of values or is dependent on one or
more parameters, such as time, then the measurands required for its description are the set of quantities
describing that distribution or that dependence.
1.3 This Guide is also applicable to evaluating and expressing the uncertainty associated with the
conceptual design and theoretical analysis of experiments, methods of measurement, and complex
components and systems. Because a measurement result and its uncertainty may be conceptual and based
entirely on hypothetical data, the term “result of a measurement” as used in this Guide should be interpreted in
this broader context.
1.4 This Guide provides general rules for evaluating and expressing uncertainty in measurement rather
than detailed, technology-specific instructions. Further, it does not discuss how the uncertainty of a particular
measurement result, once evaluated, may be used for different purposes, for example, to draw conclusions
about the compatibility of that result with other similar results, to establish tolerance limits in a manufacturing
process, or to decide if a certain course of action may be safely undertaken. It may therefore be necessary to
develop particular standards based on this Guide that deal with the problems peculiar to specific fields of
measurement or with the various uses of quantitative expressions of uncertainty.* These standards may be
simplified versions of this Guide but should include the detail that is appropriate to the level of accuracy and
complexity of the measurements and uses addressed.
ISO/IEC GUIDE 98-3:2008 history
2011ISO/IEC Guide 98-3:2008/Suppl 2:2011 Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) — Supplement 2: Extension to any number of output quantities
2008ISO/IEC GUIDE 98-3:2008/Suppl 1:2008 Uncertainty of measurement Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) Supplement 1: Propagation of distributions using a Monte Carlo method
2008ISO/IEC GUIDE 98-3:2008 Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in measurement (GUM:1995)