Physikalisch-Technische Bundesanstalt

Is the measurement result correct? You should check if you are not sure. To avoid such duplication of work is the objective of an international agreement which was signed by 38 of the 48 member countries of the Metre Convention and two international organizations during the 21st General Conference of the Metre Convention (CGPM) in Paris on October 14, 1999: the Mutual Recognition Arrangement (MRA).

The MRA – the "Arrangement on the mutual recognition of the equivalence of national standards and of calibration certificates issued by national metrology institutes" – is not a diplomatic treaty but a technical agreement. It defines the conditions on which the national metrology institutes mutually recognize the calibration of another institute.

One central point of the arrangement are new regulations for worldwide comparison measurements, so-called key comparisons, to obtain information about the degree of equivalence of national measurement standards and calibration procedures. The MRA specifies that the International Bureau of Weights and Measures (BIPM) shall publish the results of the key comparisons and collect them in a "key comparison database" which will be accessible via internet. The database will also contain statements about the measuring capabilities of the state institutes and the associated uncertainty budgets for calibrations. The key comparisons also are a fundamental tool to build confidence. The MRA requires that all national metrology institutes prove the existence of a quality system, either by a declaration of its own or by certification by a third party. The PTB has selected the self-declaration option according to ISO/IEC 17 025.