In a calibration procedure, the test uncertainty ratio (TUR) is the ratio of the accuracy tolerance of the unit under calibration to the uncertainty of the calibration standard used. (NCSL, page 2)

TUR = UUT_tolerance / STD_uncert

The TUR must be calculated using identical parameters and units for the UUC and the calibration standard. If the accuracy tolerances are expressed as decibels, percentage, or another ratio, they must be converted to absolute values of the basic measurement units. Note: The uncertainty of a measurement standard is not necessarily the same as its accuracy specification.


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