The electric kilo: Tears, joy as kilogram gets historic update

In a historic vote, more than 50 nations unanimously approved an overhaul of the international measurement system that underpins global trade and other human endeavors, uniting Friday behind new definitions for the kilogram and other units in a way they fail to do on many other issues.

Scientists, for whom the update represented decades of work, clapped, cheered and even wept as delegates gathered in Versailles one by one said "yes" or "oui" to the change, hailed as a revolution in how humanity measures and quantifies its world.

The redefinition of the kilogram, the globally approved unit of mass, was the most hotly anticipated change. For more than a century, the kilogram has been defined as the mass of a cylinder of platinum-iridium alloy kept in a high-security vault in France. That artifact, nicknamed "Le Grand K," has been the world's sole true kilogram since 1889.