Uncertainty of measurements
The uncertainty to be assigned to a measurement result has been a widely debated subject from the very beginning of modern measurements. At least two different approaches for determining the total uncertainty had been used in the past, namely the combining of uncertainties arithmetically or in quadrature (root sum of squared quantities). In 1990 the International Committee of Weights and Measures (CIPM) convened a group of experts to formulate a consistent set of rules to compute uncertainties of measurements. The group came out with a set of recommendations known as CIPM recommendations for computation of uncertainties. In 1993, the International Organization for Standardization published the recommendations in the form of a guide. The guide is now widely used and is known as the ISO Guide for Measurement Uncertainties.