CIPM MRA COMPARISON REPORTS

This report describes the third CCM key comparison of realizations of the kilogram definition based on the fixed numerical value of the Planck constant, which came into force on 20 May 2019. As for the previous comparisons, the objectives were to determine the level of agreement between realizations of the kilogram using Kibble and joule balances and the X-ray crystal density (XRCD) method and to provide input for the calculation of the third "consensus value" of the kilogram. The consensus value serves as the basis for an internationally coordinated dissemination of the kilogram and is updated after each new key comparison. Its use will continue until the CCM decides that satisfactory agreement between realization experiments has been achieved. Another objective was the determination of the reproducibility of the realization experiments by comparing the new results with those of the previous key comparisons of kilogram realizations, CCM.M-K8.2019 and CCM.M-K8.2021.
The comparison was organized by the BIPM and had ten participants. The BIPM, LNE, METAS, NIST, NRC and UME operated Kibble balances, the NIM used a joule balance and the CMS/ITRI, NMIJ and the PTB participated using ²⁸ Si spheres, the masses of which were determined with the XRCD method. These realization methods were used to calibrate 1 kg mass standards under vacuum or in air. The standards were sent (in containers filled with air) to the BIPM where they were compared with each other (in vacuum or in air, as at the participants' laboratories) and with BIPM Pt-Ir working standards. The latter were traceable to the International Prototype of the Kilogram (IPK), the mass of which served as the definition of the kilogram until 20 May 2019.
The results of the weighings at the BIPM together with the measurement results communicated by the participants allowed comparison of the values attributed to 1 kg mass standards using the realization experiments of the participants. The level of agreement between mass determinations with the realization experiments and the BIPM as-maintained mass unit, traceable to the Planck constant through the mass of the International Prototype of the Kilogram, could also be deduced.