The Bureau International des Poids et Mesures

The BIPM and the international chain of measurements

The International Bureau of Weights and Measures (in French, Bureau International des Poids et Mesures or BIPM) was created by the Metre Convention of 1875 and is located just outside Paris, France. The BIPM is an intergovernmental organization financed by those States who are signatories of the Metre Convention, and operates under the supervision of the Comité International des Poids et Mesures (CIPM).

The BIPM has a mandate to provide the basis for a single, coherent system of measurements throughout the world which is 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 international comparisons to validate the consistency of national standards (as in electricity, ionizing radiation and chemistry).

The BIPM undertakes scientific work at the highest level on a selected set of physical and chemical quantities. The major task of the BIPM is the worldwide coordination of metrology, mainly through national metrology institutes (NMIs) which continue to disseminate the chain of traceability to the SI into national accredited laboratories and finally to industry.

Scientific metrology, as undertaken at the BIPM and the NMIs, establishes and validates the comparability and accuracy of measurements. This is achieved through traceable measurement results, obtained by connecting measurement standards of known metrological behaviour through unbroken chains of measurements, preferably traceable to the SI. The SI quantities are now almost all related to quantum phenomena, such as the spectroscopic properties of atoms or, for example, the quantum Hall effect and von Klitzing constants, for which we can assume invariability with time. Relation to unchanging quantum standards also removes the need for a physical artifact as a reference which can be broken or whose values can drift with time.