Some remarks on the application of the ISO guide concerning the expression of uncertainty to the measurement instruments

After a few comments on some aspects of the ISO Guide, we address in general terms the problems situation related to the calibration and use of measurement instruments. Then some additional concepts and definitions, not explicitly given in the Guide, are discussed, concerning the calibration diagram and the calibration factor, the role of the measurement compatibility in evaluating different measurements of the same measurand, the evaluation of the traceability level in the successive steps of any measurement hierarchy chain. Finally, some different situations encountered in measurement practice (interlaboratory comparisons, calibrations at different levels of accuracy from the national standards to the calibration and testing laboratories) are analysed and discussed