The International Prototype of the Kilogram, also known as Le Grand K, was a physical object made of platinum-iridium that served as the standard for defining the kilogram. Created in 1889, it was kept at the International Bureau of Weights and Measures in France and was used to ensure consistency in mass measurements worldwide. In 2019, the definition of the kilogram changed, moving away from a physical object to a definition based on fundamental constants of nature, specifically the Planck constant. This shift aimed to improve precision and reliability in scientific measurements, making the kilogram more stable over time.