The units for mass, voltage, resistance, and electrical current in the SI

On May 20, World Metrology Day 2019, the international system of units (SI) underwent a momentous change. The philosophy behind the unit system was altered by replacing the former definitions that rely on seven base units with seven defining physical constants to be used as a basis for realizations of the units. Supported by results from decades of precise measurements, four new definitions and four fixed numerical values were assigned. In this article, we discuss the significance of this change for the unit of mass the kilogram and the electrical units ampere, volt, and ohm.