ABSTRACT
A measurement of a quantity, mass is incomplete without a quantitative statement of the uncertainty of the measurement. In the past, the uncertainty of a measurement had been considered to consist of random and systematic components. This chapter discusses the National Institute of Standards and Technology (NIST) guidelines for evaluating and expressing the uncertainty of measurement results. In October 1992, NIST instituted a new policy on expressing measurement uncertainty. The new policy was based on the approach to expressing uncertainty in measurement recommended by the International Committee for Weights and Measures and on the elaboration of that approach given in the Guide to the Expression of Uncertainty in Measurement. NIST prepared a Technical Note, “Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results,” to assist in putting the policy into practice. Each component of uncertainty is represented by an estimated standard deviation, referred to as a standard uncertainty.
