The world’s most commonly used system of measurement, the International System of Units (SI), was redefined in 2019. Since then, units have needed to be defined in terms of the constants of nature—that is, nature’s rules that are fixed and of no uncertainty, such as the speed of light—and not in terms of arbitrary references.
Click here for original story, Experiment with turnstiles of single electrons shows way towards new power standard
Source: Phys.org