How and why we redefined the kilogram

An ounce is an ounce, and a kilogram is a kilogram, but how are these units actually measured? How do your scales know how much a pound or a gram weighs?Since 1889, the kilogram’s definition has been based on a metal artifact stored under lock and key in a vault near Paris. It’s called the International Prototype Kilogram, or Le Grand K, and it is the world standard. What it weighs, the kilogram weighs. No more, no less.Le Grand K was created (along with the rest of the metric syste