Abstract. A comparison of the standards for absorbed dose to water of the Physikalisch-Technische Bundesanstalt (PTB), Germany and of the Bureau International des Poids et Mesures (BIPM) has been made in ⁶⁰Co gamma radiation under the auspices of the key comparison BIPM.RI(I)-K4. The comparison result, based on the calibration coefficients for three transfer standards and expressed as a ratio of the PTB and the BIPM standards for absorbed dose to water, is 0.9961 (0.0037). This result replaces the earlier PTB value in this key comparison. The degrees of equivalence between the PTB and the other participants in this comparison have been calculated and the results are given in the form of a matrix for the twelve national metrology institutes (NMIs) that have taken part in the ongoing comparison for absorbed dose to water. A graphical presentation is also given.

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The final report has been peer-reviewed and approved for publication by Section I of the Consultative Committee for Ionizing Radiation (CCRI(I)), according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).