International comparison of roundness profiles with nanometric accuracy

Roundness profiles are compared which were obtained from measurements carried out at five national metrology laboratories. The object used for this comparison was a zirconium-oxide sphere with a profile containing higher harmonics and a total roundness deviation of about 42 nm. The measurement results were obtained using different and independent measuring instruments and different evaluation methods for spindle error separation. The number of data points used ranged from 50 to 4096. Before the analysis, the profiles were transformed to a common digital data format containing 1024 points and a correlation analysis was carried out to determine a common zero position for the profiles. In the analysis, standard deviations and maximum deviations were calculated from point-by-point differences of the profiles with reference to one another or to the average profile. Fourier analysis was used to select a spectral area for an analysis at the edge of the significance limit. The comparison shows that each participating laboratory is able to measure a roundness profile with a standard deviation in each data point of less than 2 nm.