Final Report on CIPM key comparison of multiples and submultiples of the kilogram (CCM.M-K2)

A key comparison concerning mass determination of five mass standards has been carried out under the auspices of the Comité Consultatif pour la Masse et les Grandeurs Apparantées (CCM) from March 1998 to March 1999. The nominal values of the mass standards were 100 mg, 2 g, 20 g, 500 g and 10 kg. The fourteen participants have been divided into three groups and the corresponding three sets of standards have been circulated within the groups in parallel. The pilot laboratory, PTB, has measured the volumes, the centres of gravity and the magnetic susceptibilities of the standards before the circulation and has communicated these values to the participants. PTB has also verified the stability of all travelling standards in advance. The majority of the instabilities of the standards during their circulation were insignificant. They have been considered for the evaluation of the results. Table 1 shows the results reported by the laboratories. A first evaluation based on the combined standard uncertainties and referred to the pilot laboratory's results has shown a few outliers, see figures 1 to 5. The participants decided therefore to choose the median as a 'robust' reference value. Tables 5 to 9 show the differences and associated uncertainties between the laboratories in the form of matrices. The degrees of equivalence of the participating laboratories for each of the five mass determinations are presented in table 11 and are shown in figures 6 to 10. These results are associated with the expanded uncertainties referred to a confidence level of 95%. They show no outliers except for two at 500 g and one at 20 g. No laboratory had more than one outlier of the five results. This key comparison can therefore be considered as very successful