Worlds Roundest Object

The world s roundest object helps solve the longest running problem in measurement how to define the kilogram. A kilogram isn t what it used to be. Literally. The original name for it was the grave, proposed in 1793 but it fell victim to the French Revolution like its creator, Lavoisier. So begins the tale of the most unusual SI unit. The kilogram is the only base unit with a prefix in its name, and the only one still defined by a physical artifact, the international prototype kilogram or IPK.