See GUM. Please see "A Beginner's Guide to Uncertainty of Measurement" by Stephanie Bell. parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand. When reporting the result of a measurement of a physical quantity, it is obligatory that some quantitative indication of the quality of the result be given so that those who use it can assess its reliability. Without such an indication, measurement results cannot be compared, either among themselves or with reference values given in a specification or standard.