Special 'K': Redefining the kilogram with the help of an Ottawa lab

There was only one official kilogram weight handed down from the time of Napoleon, and by the time of France’s centennial in 1879 it was considerably bunged up.
That year, as the Eiffel Tower was going up, France commissioned several new cylinders made from mixed platinum and iridium, and chose one of these as the new official kilogram. Le Grand K, it’s called today. It defines all mass, everywhere.
Locked in a vault near Paris, it has been taken out only four times since its creatio