Stating Best Uncertainties Over a Range of Values

by David Deaver
The Guides to Measurement Uncertainty (GUMs) give very prescriptive methods for calculating measurement uncertainty at individual points. Some laboratories undertake the calculation of uncertainty at many points and state them in their Scope of Accreditation as their Calibration and Measurement Capability (CMC) values. Other laboratories attempt to simplify the effort to generate CMC values by stating them as a formula which spans a number of values. However, there is less guidance as how to use a detailed uncertainty analyses at just a few points to support a large parameter space. This paper shows some of the serious errors being made currently that result in grossly understating some uncertainties and proposes a methodology that is simple but eliminates some of these transgressions.