The importance of measurement uncertainty during gauge block calibration in determining compliance with specifications

This article deals with selected problems related to the calibration of gauge blocks. It describes basic terms and definitions concerning principles of determining the conformity of calibration results with specifications, such as measurement uncertainty and measurement traceability. The requirements for laboratories accredited according to ISO/IEC 17025:2017 were discussed that are related to the declaration of compliance with the specification. Guidelines are given on decision rules and compliance principles based on ILAC-G8:09/2019 and JCGM 106:2012 in terms of the guard bands used and the associated risks of making an erroneous decision and the application of two decision rules: binary and nonbinary. The presented problems were supported by an analysis regarding calibration of the gauge blocks by the interferometric and comparative methods with regard to measurement uncertainty and deviations of the length in relation to the nominal length for individual grades in accordance with ISO 3650:1998. As the theoretical analysis has shown, there are no sources in the literature that would allow one to assess the risk of making the wrong decision during the calibration of gauge blocks. Therefore, the authors believe that the results presented in this paper will be of interest both to researchers dealing with the problem of estimating measurement uncertainty and to the staff of measurement laboratories.