Abstract. The present definition of the unit of mass in the International System (SI) is based on the international prototype of the kilogram, an artefact dating back to the 1880s. At present there is considerable effort worldwide aimed at replacing this artefact definition by one based on physical constants. This paper gives a brief history of the SI unit and how it is currently realized. The focus is on historical information, often forgotten, which has current relevance.

Print publication: Issue 6 (December 2003)
Received 29 October 2003
Published 27 November 2003