Roundest Objects in the World Created

Roundest objects in the world created.

"Now, an international group of engineers and craftsmen has gone him one better and built a pair of nearly perfect spheres that are thought to be the roundest objects in the world." They are to be the new definition of the kilogram. "The kilogram is the only remaining standard of measurement tied to a single physical object: a 120-year-old lump of platinum and iridium that sits in a vault outside of Paris, France. But the mass of this chunk of metal is slowly changing relative to the 40-odd copies kept by other countries, and no one knows why or by how much."

I thought the kilogram was the weight of a liter of water but Wikipedia says that used to be the definition but it was changed since it's not convenient. Water evaporates. and has different densities at different temperatures. So in 1799 to an all-platinum kilogram prototype and in 1889 this was updated to the current prototype.