 In the International System of Units (SI), there remains no prototype standard since May 20, 2019.Before that date, the last prototype used was the international prototype of the kilogram, a solid platinum-iridium cylinder kept at the Bureau International des Poids et Mesures (International Bureau of Weights and Measures) in Sèvres France (a suburb of Paris) that by definition was the mass of exactly one kilogram.Copies of this prototype are fashioned and issued to many nations to represent the national standard of the kilogram and are periodically compared to the Paris prototype.