An instrument is fit for purpose if it meets the requirements of its intended use. From a metrological perspective, it is fit for purpose if the measurement uncertainty of the result is equal to or lower than the required measuring tolerance. In weighing, for example, the GWP calibration certificate compares the measured uncertainty with the user-specified weighing tolerance and thus documents fitness for purpose. A similar evaluation using estimated uncertainties is made before the purchase of a new instrument in the
GWP Recommendation document.