The Bureau International des Poids et Mesures (BIPM) has been founded by the “Meter Convention”, signed by seventeen nations in Paris on 20 May 1875. It is located at Sèvres, near Paris, France. The International Prototype of the Kilogram, the sole remaining physical prototype of an SI unit, is kept at the bureau, as well the International Prototype of the Meter. Since 1985 the Bureau is responsible for the maintainance of the French atomic time.