Supplement 2 to the Guide to the expression of uncertainty in measurement (GUM) has been published by the BIPM (Bureau International des Poids et Mesures). The supplement adds value to the GUM by providing guidance on aspects of uncertainty evaluation that are not explicitly dealt with in the original guide.

The 72-page supplement extends the provisions of the GUM to measurement models having any number of output quantities (vector measurands). Such models arise in many disciplines such as electrical, mass and temperature measurement, and are illustrated by practical examples in the supplement.

The extensions include a generalisation of the GUM's law of propagation of uncertainty and an implementation of the propagation of distributions, based on a Monte Carlo method given in GUM Supplement 1. The concept of coverage (confidence) interval is also extended to coverage regions.

NPL already provides software to support Supplement 1 and will make available software to support Supplement 2 in the future. A best-practice guide. and a software specification document, which are continually updated as part of the Mathematics and Modelling for Metrology (MMM) programme, are strongly aligned with both supplements, and the supporting software.

Background

Supplement 2 was developed by Working Group 1 (GUM) of the Joint Committee for Guides in Metrology (JCGM), which is responsible for the GUM, the VIM (International Vocabulary of Metrology), and other supporting documents.

Members of the JCGM are: BIPM, the International Electrotechnical Commission (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 Chemistry (IUPAC), the International Union of Pure and Applied Physics (IUPAP), and the International Organization of Legal Metrology (OIML).

NPL led the work on GUM Supplement 2, and previously on GUM Supplement 1, and on an introductory guide to measurement uncertainty, the GUM and other documents. Currently, NPL leads the work on GUM Supplement 3, concerned with measurement modelling, and is also editorially responsible for the GUM itself, which is currently undergoing revision.

The NPL activity is supported by the National Measurement Office of the UK Department for Business, Innovation and Skills, as part of the MMM programme.

Find out more NPL's Mathematics and Scientific Computing work.

For more information, please contact Peter Harris