From 1889 to 2019, the mass of a kilogram was defined by an object known as...
From 1889 to 2019, the mass of a kilogram was defined by an object known as the international prototype kilogram (IPK) or, less formally, Le Grand K. A kilogram was a kilogram because of this object: a platinum alloy cylinder that sits in a vault on the outskirts of Paris. Le Grand K is located in an environmentally...
