Le Grand K
Le Grand K is the physical standard for a unit of mass representing the kilogram, which is kept near Paris at the Bureau International des Poids et Mesures (BIPM, or the International Bureau of Weights and Measures, or BIPM). The kilogram is a unit in the International System of Units ("SI", meaning French Le Système International d'Unités).
Le Grand K, known more formally as the International Prototype Kilogram (IPK) is a bar of platinum-iridium alloy. It has been maintained under special conditions in a vault, dating back to the 1880s.
Scientists cannot explain why Le Grand K has been losing weight.