The kilogram, a fundamental unit of mass, has been redefined based on a constant of nature – the Planck constant – to address limitations of the old platinum-iridium standard. NIST, responsible for disseminating mass standards in the U.S., maintained prototypes like K20 and K4 until 2019. The redefinition allows for more accurate measurements, especially at smaller scales, and is supported by international collaboration.
Source: https://www.nist.gov/si-redefinition/kilogram-introduction
Keywords: Kilogram, Planck constant, NIST
