A statistically robust estimate of the true value of a reference material parameter (equivalent to the Certified Value for a CRM).

Samples sufficiently homogeneous and stable with respect to one or more specified properties, which have been established to be fit for its intended use to check results for specific methods in a measurement process. RM’s may be chemicals, solutions, gas mixtures, matrix reference materials, physico-chemical reference materials, objects or biological specimens. The essential difference between an RM and a CRM is that the CRM is characterised by a metrologically valid procedure for one or more specified properties, accompanied by an RM certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability.

The closeness of agreement between results for the same parameter carried out by the same method, by the same operator, with the same instrument, in the same laboratory, over a short interval of time.

The closeness of agreement between results for the same parameter carried out by a different method, or different operator, or different instrument, or in a different laboratory, or over an interval of time quite long in comparison to the duration of a single measurement.