A Necessary Correction in Uncertainties Computation

Abstract

Both in Physical and in Loyal metrology, uncertainties are computed following International Vocabulary of Metrology (VIM) and the Guide for Expression of Uncertainty in Measurement (GUM). There are three causes for uncertainty, in strument reading (resolution), instrument accuracy (error) and dispersión of results when measurement is repeated. (precision), togheter form the combined uncertainty Uc, its variance (Uc squared) is the sum of the variances for resolution, error and precision. Even reading is not an aleatory process, VIM/GUM asociates it to a rectangular distribution, its variance being 1/3 of squared resolution. If a “reading” is the difference between “measurement” and “0” reading, its uncertainty must be computed by a triangular distribution, with duplication of the variance as compared with rectangular. In the present work, the impact on callibration and adjustement procedures, is discuted, different situations and criteria for application of the proposed correction, are explored, but we ever recommend its use.