The Kilogram
The kilogram is the base unit of mass in the International System of Units.
It is defined in the late modern era by setting the fixed numerical value of Planck's constant to 6.62607015 x 10-34.
Previously, the kilogram was defined by the weight of a platinum/iridium ingot named "Le Grand K", jealously guarded in France.
Le Grand K was the standard for the kilogram from 1889 to 2019, when the switch to a definition by physical constant was made.
Le Grand K, in all its objective glory.