For nearly 130 years the definition of the kilogram has been tied to a lump of metal inside a Parisian vault that varies in mass from decade to decade. Now all that is about to change ...

It’s one of those things where if you think about it too much, your head might explode. We know there are 1,000 grams in a kilogram, and 1,000 kilograms in a metric ton, but how was it ever ...