Abstract. The COOMET.T-K3 comparison is the regional comparison of the defining fixed points realization in the range from the triple point of water to the freezing point of zinc. Four national metrology institutes—VNIIM (pilot), SMU, BelGIM and NNC IM—took part in the COOMET regional comparisons. At the first stage the cells of fixed points of the national metrology institutes were used as transfer standards. They were compared with the VNIIM cells by means of standard platinum resistance thermometers using the VNIIM standard setups and equipment. At the second stage the equivalence of realization of the fixed points at the national institutes was estimated. A standard platinum resistance thermometer SPRT (25 ohm), manufactured at VNIIM, was used as a transfer standard.

The degree of equivalence of the measurement standard of the national metrology institutes participating in the COOMET comparison is determined relative to the reference values of the CCT-K3 through the measurement results received in the linking national metrology institutes, VNIIM and SMU, which took part in both comparisons. The values 'ARV' of K3 were assumed as the reference values. The report presents the results of this comparison and gives detailed information about the method of estimation of the degree of equivalence of NMI standards and its uncertainty.

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The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).