Standard uncertainty in each measurement result explicit or implicit

Abstract

Concepts given in the ISO Guide will have the chance to be used widely in science, engineering, industry and commerce only if their realizations will be simple enough. According to the ISO Guide the complete statement of a measurement result should contain information about standard uncertainty of measurement. Because the uncertainty was traditionally expressed as confidence interval, the ISO Guide also allows expression of uncertainty by the so-called expanded uncertainty. The author proposes that expanded uncertainty should not be used because it complicates the estimation of combined uncertainty and can cause misunderstandings. The user of measurement results should multiply the standard uncertainty with the coverage factor which is appropriate for their particular application. The uncertainty of a measurement result should always be expressed by standard deviation only. As the consequence, the estimation of measurement uncertainty will be simpler and the quality of measurement results directly comparable. In everyday routine work measurement result is expressed by measured value (the best approximation of the measurand) without measurement uncertainty. The author proposes the method of rounding off the measurement result on the basis of its total measurement uncertainty. A properly rounded off measurement result contains the information about measurement uncertainty. The user of a measurement result will be able to estimate total measurement uncertainty on the basis of the number of significant digits of measurement result.