ISO/IEC Guide 98-3:2008

Overview

ISO/IEC Guide 98-3:2008 is the reissued Guide to the Expression of Uncertainty in Measurement (GUM:1995) with minor corrections. It establishes internationally accepted principles and general rules for evaluating and expressing measurement uncertainty that apply across sectors and levels of accuracy - from shop-floor measurements to fundamental research. The Guide supports traceability, comparability of results, and transparent reporting of measurement quality.

Key topics

• Fundamental concepts: measurand, error, uncertainty, corrected value, and practical considerations for measurements.
• Modeling the measurement: identifying input quantities and relationships used to obtain a measurement result.
• Evaluating standard uncertainty: two complementary approaches
  • Type A - statistical evaluation from repeated observations.
  • Type B - evaluation from other information (calibration certificates, manufacturer specifications, expert judgment).
• Combining uncertainties: procedures for determining combined standard uncertainty, including treatment of correlated and uncorrelated input quantities.
• Expanded uncertainty: converting combined standard uncertainty into an interval (using a coverage factor) for reporting at a stated level of confidence.
• Reporting: guidance on documenting measurement results, uncertainty statements, and complete information for traceability and reproducibility.
• Supporting material: annexes with worked examples, glossary of symbols, statistical background, and practical guidance on evaluating components and degrees of freedom.

Applications

ISO/IEC Guide 98-3:2008 is used wherever reliable, comparable measurement results are required:

• Quality control and quality assurance in manufacturing and production.
• Calibration laboratories and national measurement institutes for establishing traceability.
• Regulatory compliance and enforcement where legally defensible measurement statements are needed.
• Scientific research and R&D to quantify measurement reliability.
• Development and comparison of reference standards and reference materials.

Who should use it

• Metrologists and calibration engineers
• Laboratory managers and quality assurance professionals
• Test and measurement engineers in industry and research
• Accreditation and conformity assessment bodies
• Regulators and standards developers

Related standards and organizations

The Guide is the internationally accepted foundation for expressing uncertainty and is closely associated with metrology organizations such as BIPM, JCGM, IEC, ISO and OIML. It is intended to be used in conjunction with national and international calibration, accreditation and measurement-system standards and best practices that require documented uncertainty evaluations.

Keywords: GUM, ISO/IEC Guide 98-3:2008, uncertainty of measurement, measurement uncertainty, standard uncertainty, combined standard uncertainty, expanded uncertainty, Type A, Type B, traceability, calibration, metrology.