Base Units of the Système International d'Unités, their Accuracy, Dissemination and International Traceability

An outline is given of the organizational structure of the Convention du Mètre, the basis for international agreement on units of measurement, followed by a brief discussion on why accurate measurements are required. The Système International d'Unités (SI) is introduced and the definition and practical realization of each of its base units are discussed. Prospects for improvements in their practical realizations and, in the case of the kilogram, prospects for a new definition based on atomic or fundamental constants are outlined.