The international kilogram crisisA copy of the international prototype kilogram under its protective casing. The real prototype, known as Le Grand K, is rarely removed from its temperature- and humidity-controlled vault to avoid damage.
In the 120 years since several dozen cylinders were crafted in France to serve as the world's standards of the kilogram, they have been mysteriously drifting apart. The result is a race to redefine the measure.
http://www.latimes.com/news/science/la-sci-kilogram17apr17,0,1071730.story
