Error, uncertainty and probability

There is much confusion on the topic of uncertainty of measurement. Yet, measurement uncertainty is both a pivotal concept in measurement theory and, above all, a basic requisite in practice, from the physics laboratory measuring some exotic property of Nature to the shop floor. The purpose of this paper is to give the author's view on measurement uncertainty in an unambiguous way, thus privileging clarity over diplomacy, for which he apologizes once and for all. Accordingly, the scope of the paper is to discuss the fundamental metrological concepts and associated terms, as given in the International Vocabulary of Metrology, VIM, in the light of their relevance to the topic of uncertainty, as treated in the Guide to the expression of uncertainty in measurement, GUM. In this scheme, the focus is on the concepts of error and uncertainty and on their intimate connection, often masked by misunderstanding when not buried under the misconception that they are opposite and competing concepts. It will be shown that probability theory is the correct framework in which error and uncertainty are reconciled in a convenient and rigorous way. The author is convener of the Joint Committee for Guides in Metrology (JCGM) Working Group 1 (GUM). The opinion expressed in this paper does not necessarily represent the view of this Working Group.