How and Why the Kilogram Value Changed

At this year’s General Conference of Weights and Measures, a collective of 60 countries voted to change the kilogram’s value. Up until this vote, the kilogram was based on a platinum and iridium fragment, called the “Le Grande K,” which is stored in a chamber in the International Bureau of Weights and Measures in Sèvres, France. Over time, Big K seemed to be losing weight—or its replicas …