Review of the international measurement system
June 15, 2018
The revised SI will be approved by the 26th General Conference on Weights and Measures (GFCM) in November 2018, coming into force on World Metrology Day, on May 20, 2019.
Consequences of the review of the IS:
The kilogram, the ampere, the kelvin and the mole will continue to be the units of mass, electric current intensity, thermodynamic temperature and quantity of substance, but their definitions will be based on constants.
The revised definitions of the kilogram, ampere, kelvin and mol will have no impact on the second, the meter and the candela.
The revised SI will have a greater influence on high levels of accuracy. All the practical realizations of the units will be supported by constants and will be reproducible in time and space.
The definitions will be separated from their realization, which will allow the evolution of the practical realizations, while the definitions endure over time.
Improves the use of SI in some scientific measurements, while reducing the uncertainties of many fundamental constants.
The new definition of the kilogram ensures the long-term stability of the SI unit of mass, allowing its realization at any time and place.
After the revision of the SI, it will inherit the relative uncertainty of h.
The uncertainty of the electrical quantities is reduced, integrating them in the SI.
The new definition of kelvin will be feasible through different experiments and over a wide range of temperatures. The thermodynamic temperature of the triple point of the water TTPW will be exactly 273.16 K, but with a relative uncertainty equal to the recommended value of k just before the redefinition. Thereafter, the value of TTPW will be determined experimentally.
The redefinition of the mole with respect to an exact numerical value of the Avogadro NA constant frees it from its dependence on the kilogram and makes the distinction between "quantity of substance" and "mass" more visible.