At its meeting in Prague in October 1999, the EUROMET Technical Committee for Length, TC-L, decided upon a supplementary comparison on gauge block measurements, numbered EUROMET.L-S12, with the National Metrology Laboratory Ireland (NML) as the pilot laboratory. NPL, UK, agreed to act as co-pilot and linking laboratory to the corresponding key comparison, EUROMET.L-K1, by making both mechanical comparison and interferometric measurements. The comparison was subsequently registered as EUROMET project 601.

This report describes the results of measurements of eight gauge blocks at thirteen European national metrology institutes. This comparison was carried out during the period from April 2001 to September 2002.

The primary measurement quantity was the deviation of the central length of the gauge block from its nominal length, as defined in ISO 3650. The central length was determined by mechanical comparison against the laboratory reference gauge blocks using an appropriate mechanical comparator. Where possible, the participants also determined the variation in length across the surface of each gauge by undertaking measurements at five points on the surface of each gauge against the central length of the laboratory reference gauge block.

The results obtained show a good overall agreement of measurement results with the calculated mean values. The uncertainties claimed in the CMC tables are broadly in line with those achieved in this supplementary comparison.

Main text. 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 kcdb.bipm.org/.

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