Evaluation of regional key comparison data: two approaches for data processing

This paper deals with the problem of establishing degrees of equivalence for national measurement standards participating in regional key comparisons (RMO KC), with respect to a key comparison reference value (KCRV), using measurement results obtained by linking national metrology institutes (NMIs). Two types of key comparisons are considered, which differ in applying either a material measure or a measuring instrument as a travelling measurement standard. The results obtained by linking NMIs are used to determine transformation procedures for measurement results of the RMO KC so that the transformed results can be compared directly with CIPM KC results. Formulae are given for evaluating the degrees of equivalence of the national measurement standards of laboratories participating in the RMO KC, with respect to the KCRV, taking into account possible correlations between measurement results.