Proposal for linking the results of CIPM and RMO key comparisons

A procedure for linking the results of a Regional Metrology Organisation (RMO) key comparison to those of a related Comité International des Poids et Mesures (CIPM) key comparison is proposed. The RMO results are linked to the CIPM results by a factor which is determined as the ratio of the CIPM key comparison reference value and the weighted mean of the RMO results of the linking laboratories. Correlations of the results of the linking laboratories in the two comparisons are taken into account. The uncertainties associated with the linked RMO results and the degrees of equivalence (DOEs) are explicitly given. The influence of correlations of the results of the linking laboratories in both comparisons is examined. It is shown that these correlations can decrease the linking uncertainty, whereas DOEs are expected to be influenced less. The proposed linking procedure is illustrated by its application to linking the results of a recent CIPM key comparison on accelerometer calibrations to that of a corresponding RMO key comparison.