Update of the BIPM comparison BIPM.RI(II)-K1.Co-57 of activity measurements of the radionuclide 57Co to include the 2013 result of the POLATOM (Poland), the 2015 result of the NMISA (South Africa), the 2021 result of the CMI (Czech Republic), and to link the CCRI(II)-S6.Co-57 comparison

Main text Three new participations in the BIPM.RI(II)-K1.Co-57 comparison have been added to the previous results and this has produced a revised value for the key comparison reference value (KCRV), calculated using the power-moderated weighted mean. A link has been made to the CCRI(II)-S6.Co-57 comparison piloted by the International Atomic Energy Agency (IAEA) in 2008 for which one sample of the 57Co radioactive solution was sent to the SIR. Two NMIs used the S6 comparison to update their degree of equivalence. The degrees of equivalence between each equivalent activity measured in the International Reference System (SIR) and the KCRV have been calculated and the results are given in the form of a table for the remaining seven NMIs in the BIPM.RI(II)-K1.Co-57 comparison and the three eligible participants in the CCRI(II)-S6.Co-57 comparison. A graphical presentation is also given. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).