Final report on EUROMET.L-K4: Calibration of diameter standards, Group 1

KEY COMPARISON At its meeting in October 2003, the EUROMET (now EURAMET) Technical Committee for Length, TC-L, decided upon a key comparison on diameter standards. Due to the large number of participants, it was decided to have two groups arranged according to the claimed uncertainties. Eleven laboratories from EURAMET and two laboratories from other RMOs participated in the group 1. The circulation of the gauges started in June 2005. The comparison was registered as EUROMET project 812. The final report for the group 1 describes the results of measurements of five diameter standards (one sphere, two rings and two plugs). A third plug was added for optional measurements. The main measurand was the diameter of each gauge at 20 ºC and corrected to zero force. The diameter was measured at three heights of each cylindrical gauge. As requested by the protocol, laboratories also provided the departure from roundness of the sphere. Participants were invited also to report the roundness and the straightness of the cylindrical gauges. The reference values were calculated from the weighted mean of the larger consistent subset of results according to the Birge ratio criteria. In general, the overall agreement was good, with some larger spread of results for the plugs.