The idea of performing a comparison of squareness resulted from the need to review the MRA Appendix C, Category 90° square. At its meeting in October 1999 (in Prague) it was decided upon a first comparison of squareness measurements in the framework of EUROMET, numbered #570, starting in 2000, with the Slovak Institute of Metrology (SMU) as the pilot laboratory.

During the preparation stage of the project, it was agreed that it should be submitted as a EUROMET supplementary comparison in the framework of the Mutual Recognition Arrangement (MRA) of the Metre Convention and would boost confidence in calibration and measurement certificates issued by the participating national metrology institutes.

The aim of the comparison of squareness measurement was to compare and verify the declared calibration measurement capabilities of participating laboratories and to investigate the effect of systematic influences in the measurement process and their elimination.

Eleven NMIs from the EUROMET region carried out this project. Two standards were calibrated:

• granite squareness standard of rectangular shape,
• cylindrical squareness standard of steel with marked positions for the profile lines.

• granite squareness standard: interior angle γ_B between two lines AB and AC (envelope – LS regression) fitted through the measured profiles,

• granite squareness standard: interior angle γ_LS between two LS regression lines AB and AC fitted through the measured profiles,
• cylindrical squareness standard: interior angles γ_0°, γ_90°, γ_180°, γ_270° between the LS regression line fitted through the measurement profiles at 0°, 90°, 180°, 270° and the envelope plane of the basis (resting on a surface plate),
• local LS straightness deviation for all measured profiles (2 and 4) of both standards.

Graphical interpretations of all deviations are contained in the Final Report. In order to compare the individual deviations mutually (25 profiles for the granite square and 44 profiles for the cylinder), graphical illustrations of 'standard deviations' and both extreme values (max. and min.) of deviations were created.

This regional supplementary comparison has provided independent information about the metrological properties of the measuring equipment and method used by the participating NMIs.

The Final Report does not contain the En values. Participants could not estimate some contributions in the uncertainty budget on the basis of previous comparisons, since no comparison of this kind had ever been organized. Therefore the En value cannot reflect the actual state of the given NMI. Instead of En, an analysis has been performed by means of the Grubbs test according to ISO 5725-2.

This comparison provided information about the state of provision of metrological services in the field of big squares measurement.

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 Mutual Recognition Arrangement (MRA).