This article talks about Measurement Uncertainty , which some of the various values obtained experimentally or derived by calculation or theory turn out to be wrong, all of them must be assigned to the measurand. Uncertainty is a measure for the width of the range derived from these data and, together with an appropriate mean value as the result of measurement, describes the level of knowledge about the measurand. Because of our limited knowledge it is quite possible that the uncertainty is underestimated due to missing uncertainty components.