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The scientific activity of the laboratories of the BIPM is divided
in relation to the units of the SI into:
– length;
– mass;
– time;
– electricity;
– ionizing radiations;
– chemistry.
The CIPM (the International Committee for Weights and
Measures) supervises and guides the BIPM’s work and it is itself
under the authority of the Conférence Générale des Poids et Mesures
(CGPM). The CGPM is composed of delegates (51 in 2004) from all
the states, which have signed the Treaty of the Metre Convention. The
CGPM meets every four years and its mission is, in particular:
– to debate and prompt the necessary steps to bring about the
propagation and the improvement of the SI;
– to approve the results of the new basic metrological
determinations and adopt the various scientific resolutions of
international significance.
At the conference 18 members of the CIPM are elected, half of
which are reelected every four years.
In October 1999, the directors of the national metrology institutes
(NMI) of the states belonging to the Metre Convention signed an
arrangement (MRA) to mutually recognize the national measurement
standards and the calibration and measurement certificates issued by
their laboratories. In order that the criteria of mutual recognition be
unbiased, the agreement is based on, first, the results of a set of key
comparisons carried out according to specified methods that lead to a
quantitative assessment of the degree of equivalence of the national
measurement standards; secondly, the setting up by each NMI of
appropriate means so as ensure the quality of the measurements; and
thirdly, the actual participation of each NMI in suitable additional
comparisons. This agreement is in two parts: in the first part, the
signatories recognize the degree of equivalence of the national
measurement standards of the participating national laboratories; in
the second part, the signatories recognize the validity of the
calibration and measurement certificates delivered by the participating
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