The 26th International Conference on Weights and Measures held in Versailles, France, adopted a resolution to revise the International System of Units (SI). The four basic units in the International System of Units were changed to be defined by natural constants and officially came into effect on the International Day of Metrology in 2019 (May 20). At this point, all 7 basic units of the International System of Units will be defined by basic physical constants.
These four basic units are: the mass unit kilogram, the current unit ampere, the amount of substance unit mole, and the temperature unit Kelvin. Among them, the kilogram is defined by Planck’s constant, the ampere is defined by the basic charge, the mole is defined by Avogadro’s constant, and the kelvin is defined by Boltzmann’s constant.
Although people will not see much change in the quantization of basic units on the surface, it is crucial to the development of high-precision technology.
