– the intergovernmental organization through which Member States act together
     on matters related to measurement science and measurement standards.
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BIPM policy on stating uncertainties

The uncertainty associated with BIPM calibrations is a combined standard uncertainty, without the application of a coverage factor k.

This long-standing practice of not applying a coverage factor is considered to facilitate the combination of the BIPM and NMI uncertainties, and thus simplify the subsequent dissemination of the standard to the customers of the NMI. It can be assumed that the BIPM's measurements fulfil the criteria of section G6.6 of the GUM. In particular, for the purpose of calculating the expanded uncertainty for their end result at a specified level of confidence, an NMI can assume that the number of effective degrees of freedom for a BIPM calibration is sufficient to be able to use a coverage factor k = 2 for a level of confidence of approximately 95 %. Any exceptions are noted in the calibration certificate.

This policy was endorsed by the CIPM at its 93rd meeting (2004).

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BIPM policy on stating uncertainties
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