Abstract

The revised SI, which came into force on May 20th, 2019, bases the system of units on fixed numerical values of constants of nature, so-called "defining constants". An overview of the changes implemented by the revised SI will be presented with an emphasis on the consequences for the unit candela and the unit second; namely, the realization of a traceable, quantum-based candela and a possible redefinition of the unit second. Prospects of time scales and time and frequency transfer will be given.

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