Over the years, the kilogram has added, well, a few grams. Not really whole grams, actually micrograms. But a group of scientists are trying to undo that weight gain because kilograms are one of the few units of measure still defined using physical artifacts.
What exactly is a kilogram? The best way to find out is to peer into a vault maintained by the International Bureau of Weights and Measures in France. Inside that vault rests a cylindrical chunk of metal known as the kilogram “standard.” It’s been there since the late 1800s, and it serves as the authoritative kilogram. […]