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BIPM

The Metre Convention and the BIPM

The Metre Convention is the treaty that was signed 20 May 1875 by 17 countries, including Denmark, to address the need for a uniform system of measures and weight.

The International Bureau of Weights and Measures (Bureau International des Poids et Mesures – BIPM) was set up by the Metre Convention. The BIPM is an intergovernmental organization, with headquarters near Paris, France, under the authority of the General Conference on Weights and Measures (Conférence Générale des Poids et Mesures  – CGPM),  and the supervision of the International Committee for Weights and Measures (Comité International des Poids et Mesures – CIPM).

The mandate of the BIPM is to provide the basis for a single, coherent system of measurements throughout the world, traceable to the International System of Units (SI). This task takes many forms, from direct dissemination of units (as in the case of mass and time) to coordination through international comparisons of national measurement standards (as in electricity and ionizing radiation).

As of  November 2018, there are 59 Member States (formally known as “States Parties to the Metre Convention”) and 42 Associate States and Economies.

As a signatory to the Metre Convention, Denmark participates in the General Conference on Weights and Measures (CGPM). In order to support the CGPM a number of consultative committes have been etstablished. DFM is a member of the Consultative Committee for Acoustics, Ultrasound and Vibration (CCAUV), and the Consultative Committee for Amount of Substance: metrology in chemistry (CCQM). In addition to this DFM is also represented in a number of the working groups under the consultatice committees.

Read more about the Metre Convention and the BIPM here.

 

Revision of the SI

The recommended practical system of units of measurement is the International System of Units (Système International d’Unités, with the international abbreviation SI). The SI is defined by the SI Brochure, which is published by the BIPM.

At the 26th meeting of the General Conference on Weights and Measures (CGPM) in 2018 it was decided that all SI units should be defined in terms of constants that describe the natural world.

In the revised SI four of the SI base units – the kilogram, the ampere, the kelvin and the mole – are now redefined in terms of constants; the new definitions are based on fixed numerical values, respectively the Planck constant (h), the elementary charge (e), the Boltzmann constant (k), and the Avogadro constant (NA).

The new definitions entered into force on 20 May 2019.