NPR Science: Say Au Revoir To That Hunk Of Metal In France That Has Defined The Kilogram.

“The world is about to say au revoir to Le Grand K, a cylinder of platinum and iridium that has long reigned over the world’s system of weight measurement.

Le Grand K was forged in 1879 and is held in a locked vault outside Paris — revered and kept under lock and key because its mass, a little over 2 pounds, is the official definition of the kilogram.

But this is will soon change. On Friday, the international General Conference on Weights and Measures will meet in Versailles, France, to vote on whether to redefine the kilogram.

The vote is expected to be unanimous, a mere formality after years of work. Going forward, the world’s system of mass measurement will not be based on some special hunk of metal, but rather on unalterable features of the universe — such as the speed of light, time and Planck’s constant, a number that helps scientists figure out the energy of a photon of light, given its wavelength.”