The article discusses the recent redefinition of four fundamental SI units – the kilogram, ampere, kelvin, and mole – by the world’s measurement experts at a meeting in Versailles, France. This redefinition, which took effect on May 20, 2019, is based on fixed values for seven fundamental constants of physics, making it possible for anyone to make precise measurements using the International System of Units (SI) without relying on physical artifacts.
The new definitions:
1. Kilogram: Defined based on the Planck constant, allowing mass to be measured at any magnitude using a Kibble balance.
2. Ampere: Defined based on the elementary charge, making it possible to measure electric current directly.
3. Kelvin: Defined based on the Boltzmann constant, enabling temperature measurement at the quantum level.
4. Mole: Slightly edited definition based on the Avogadro number, which is now exactly defined.
These changes will make it easier and more accessible for industries to measure these units accurately, ultimately empowering them with the power of precise measurements at a lower cost. NIST is also working on developing “NIST on a Chip” technologies, which are working standards that never need calibration, to further expand access to accurate measurement devices in various industries.
Keywords: Metrology, Precision, Measurements, Standards, Units
