Abstract. An indirect comparison of the standards for the quantity absorbed dose to water was carried out between the Van Swinden Laboratorium (VSL) and the Bureau International des Poids et Mesures (BIPM) in September 2005. The comparison was based on the calibration coefficients determined for three NE2611A type ionization chambers under reference conditions in the ⁶⁰Co beams of both institutes. The comparison result, reported as a ratio of the VSL and the BIPM evaluations, is 0.9926 with a relative standard uncertainty of 4.9 × 10⁻³. This result replaces the previous indirect comparison result obtained in 2000 for the ongoing BIPM.RI(I)-K4 comparison. The degrees of equivalence for the VSL standard and the nine other national metrology institutes in this comparison are presented in the form of a matrix, together with those of a linked regional comparison. The opportunity was also taken to undertake a pilot study using the VSL water calorimeter at the BIPM.

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