Value indicating the dispersion of the possible true values of the measurement.

It is calculated from the combined uncertainty u, which is obtained by taking into account all uncertainty components that have influence in that particular measurement. Calibrations are presented with the expanded uncertainty value U, which is calculated by multiplying the combined uncertainty by a parameter k adequate to ensure a predefined level of confidence.

On the ISO 17025 calibration certificate, the value k=2 is used to achieve a 95% confidence level.