Usage of the uncertainty of measurement by accredited calibration laboratories when stating compliance

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First, concepts to state compliance with specifications are presented when taking into account the uncertainty of measurement. Then, the methods used by accredited calibration laboratories, especially within the Deutscher Kalibrierdienst (DKD), are introduced and compared with these methods and concepts. Compliance can only be stated with some probability (risk), which can be calculated by integration, if the measurement results and its probability density functions are known. A scheme for the calculation of the risks by the Monte Carlo method leads to zones of correct and false acceptance, and correct and false rejection. The user of the device under test or calibration has to decide which risk is acceptable. A statement of compliance should only be made if the measurement capability index is not smaller than about 2. The correspondence of probabilities of compliance and guard bands is shown. The rules of ISO 14253-1 and DKD-5 are equivalent to the usage of a guard band of special width. Finally, the performance criteria for comparisons in calibration are treated briefly. Their use has some similarity to the decisions made on compliance.