EN ISO/IEC 17 025: Requirements for the Estimation of Uncertainty

A calibration laboratory, or a testing laboratory performing its own calibrations, shall have and apply a procedure to estimate the uncertainty of measurement for all calibrations and for all types of calibration. The standard provides further explanation given below.

Testing laboratories shall also have and apply procedures for estimating uncertainties of measurement, except when the test methods preclude such rigorous calculations. In certain cases it is not possible to undertake metrologically and statistically valid estimations of uncertainty of measurement. In these cases the laboratory shall at least attempt to identify all the components of uncertainty and make the best possible estimation, and ensure that the form of reporting does not give an exaggerated impression of accuracy.

When estimating the uncertainty of measurement, all uncertainty components which are of importance in the given situation shall be taken into account using accepted methods of analysis.

Sources contributing to the uncertainty include, but are not necessarily limited to, the reference standards and reference materials used, methods and equipment used, the environmental conditions, the condition of the item being tested or calibrated and the operator.

The predicted long-term behavior of the tested and/or calibrated item is normally not taken into account when estimating the measurement uncertainty.

For further information see ISO 5725-1 and the Guide to the Expression of Uncertainty in Measurement (see bibliography).