The measurement uncertainty is a feature of an accredited procedure. It describes to what extent a measurement can be traced to national standards and ultimately to International System of Units (SI units). Usually, an extended
measuring uncertainty is specified, which is calculated from the standard uncertainty multiplied with the extension factor k=2.
Each measuring value is associated with a (measurement) uncertainty. In the calibration hierarchy, testing equipment on a higher level has a lower measuring uncertainty that that on a lower level.
Accreditation in line with EN ISO/IEC 17025 requires that measurement uncertainties are calculated according to EA-4/02 „Guide to Expression of the Uncertainty of Measurement in Calibration, GUM".