ABSTRACT
A measurement of a quantity, volume flow rate is incomplete without a quantitative statement of the uncertainty of the measurement. The random component has generally been considered to be a measure of precision of the measurement process as applied to the specific measurement. 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. In the International Committee for Weights and Measures and NIST approach, the several components of the uncertainty of the result of a measurement may be grouped into two categories according to the method used to estimate the numerical values of the components.
