Uncertainty of gauge block calibration by mechanical comparison: A worked example for gauge blocks of dissimilar materials

The definition of gauge block length, and the lowest-uncertainty gauge block calibrations, derive their link to the definition of the metre through the technique of optical interferometry using calibrated optical wavelengths. Following interferometric calibration of gauge blocks, the technique of mechanical comparison of gauge blocks is largely used for the dissemination of the metre. A measurement scenario for the case of low-uncertainty gauge block calibration in which the working standard and client gauge blocks are made of dissimilar materials is described. The correction for stylus deformation is determined experimentally. A detailed tutorial on evaluating the uncertainties for this gauge block calibration in accordance with the ISO Guide to the expression of uncertainty in measurement is reported, including discussion of degrees of freedom and correlations.