Realizing the Kilogram from the Planck Constant: The Kibble Balance and the Electrical Units

The international System of Units (SI) was redefined in 2018 [1]. This historical event implemented a beautiful idea—a system of units defined entirely by constants of nature. The most notable modification to the SI involved abandoning the artifact definition of the kilogram in favor of fixing the numerical value of the Planck constant. Apart from its physical and mathematical elegance, the new SI solves the problem of providing an absolute reference for the kilogram. But, how do we understand the link between the kilogram and the Planck constant? And, how can we realize the kilogram now, using the new definition? This paper attempts to give a simple answer to these complicated questions.