DD ISO/TS 21749:2005

Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Statistical methods of uncertainty evaluation
  4.1 Approach of the Guide to the expression of uncertainty
      of measurement
  4.2 Check standards
  4.3 Steps in uncertainty evaluation
  4.4 Examples in this Technical Specification
5 Type A evaluation of uncertainty
  5.1 General
  5.2 Role of time in Type A evaluation of uncertainty
  5.3 Measurement configuration
  5.4 Material inhomogeneity
  5.5 Bias due to measurement configurations
6 Type B evaluation of uncertainty
7 Propagation of uncertainty
  7.1 General
  7.2 Formulae for functions of a single variable
  7.3 Formulae for functions of two variables
8 Example - Type A evaluation of uncertainty from a gauge study
  8.1 Purpose and background
  8.2 Data collection and check standards
  8.3 Analysis of repeatability, day-to-day and long-term effects
  8.4 Probe bias
  8.5 Wiring bias
  8.6 Uncertainty calculation
Annex A (normative) Symbols
Bibliography

Gives methods for obtaining uncertainties from single-, two- and three-level nested designs only. Applies to a wide variety of measurements, for example, lengths, angles, voltages, resistances, masses and densities.

This Technical Specification follows the approach taken in the Guide to the expression of the uncertainty of measurement (GUM) and establishes the basic structure for stating and combining components of uncertainty. To this basic structure, it adds a statistical framework using the analysis of variance (ANOVA) for estimating individual components, particularly those classified as Type A evaluations of uncertainty, i.e. based on the use of statistical methods. A short description of Type B evaluations of uncertainty (non-statistical) is included for completeness.

This Technical Specification covers experimental situations where the components of uncertainty can be estimated from statistical analysis of repeated measurements, instruments, test items or check standards.

It provides methods for obtaining uncertainties from single-, two- and three-level nested designs only. More complicated experimental situations where, for example, there is interaction between operator effects and instrument effects or a cross effect, are not covered.

This Technical Specification is not applicable to measurements that cannot be replicated, such as destructive measurements or measurements on dynamically varying systems (such as fluid flow, electronic currents or telecommunications systems). It is not particularly directed to the certification of reference materials (particularly chemical substances) and to calibrations where artefacts are compared using a scheme known as a “weighing design??. For certification of reference materials, see ISO Guide 35^[14].

When results from interlaboratory studies can be used, techniques are presented in the companion guide ISO/TS 21748^[15]. The main difference between ISO/TS 21748 and this Technical Specification is that the ISO/TS 21748 is concerned with reproducibility data (with the inevitable repeatability effects), whereas this Technical Specification concentrates on repeatability data and the use of the analysis of variance for its treatment.

This Technical Specification is applicable to a wide variety of measurements, for example, lengths, angles, voltages, resistances, masses and densities.