The Mutual Recognition Arrangement of the CIPM indicates that a metrological equivalence of national measurement standards and calibration certificates issued by national metrology institutes (NMIs) should be established by a set of key comparisons chosen and organized by the Consultative Committees of the Comité Internationale des Poids et Mesures on key techniques. The CCL (Comité Consultative de Longueur), identified several key comparisons in the field of dimensional metrology. In particular, it decided that a coordinate measuring machine (CMM) two-dimensional (2-D) artifact should be carried out. CENAM (Centro Nacional de Metrología) was designated as pilot laboratory and NMIs of signatories of the Metre Convention were invited to participate. The comparison is aimed to support the Calibration and Measurement Capabilities (CMCs) claims of NMIs for CMM 2-D standards calibration.

Twelve NMIs from four Regional Metrology Organizations finished the comparison and one withdrew. The final participants were as follows:

1. NMIA (CSIRO), Australia
2. INMS-NRC, Canada
3. NIM, China
4. CMI, Czech Republic
5. BNM-LNE, France
6. PTB, Germany
7. NMIJ (NRLM), Japan
8. NMi, Netherlands
9. VNIIM, Russia
10. NPL, United Kingdom
11. NIST, USA (1)
12. CENAM, Mexico (1).

A Draft B report was circulated among the participants and, after review and approval by all of the participants, it became the final report. It comprises all the information about the comparison: the measurement results, the choice of a Key Comparison Reference Value, the estimation of its uncertainty, the performance of each participant with respect to this value and the Birge ratio for each measurand of the two artifacts.

It was decided afterwards at CCL that the exercise be classed as a supplementary comparison but the reference of CCL-K6 was kept.

In an Appendix the equivalences of all measurands of each laboratory with respect to the reference value are reported for both artifacts, as well as the pairwise equivalences between laboratories for all measurands of both artifacts. The results are shown on tables as well as in plots.

The comparison was scheduled to start in January 2001 and span the circulation until December 2002. The circulation scheme was delayed for many reasons. It finally ended in September 2004.

The following main conclusions may be drawn:

• The comparison was a valuable exercise and produced valid results as the artifacts proved to be stable throughout the comparison exercise. Therefore, the results obtained may be taken as a proof of the performance of the participants in CMM 2-D standards calibration as declared in their corresponding CMCs.
• Out of the twelve participants, ten were in good agreement for the Steel Ball Plate and nine for the Zerodur Bore Plate. The KCRV was determined from these values.
• The Birge ratios obtained for the measuring elements of both artifacts proved that there is consistency between the results obtained at the declared uncertainties of the participants. However, it would seem that the uncertainty declarations in general were rather conservative.
• The results on the Steel Ball Plate were slightly better than those on the Zerodur Bore Plate. As a conclusion, the participants are a little bit better at measuring steel artifacts than Zerodur ones.

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 the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).