The current definition of the kilogram according to the International System of Unites (called the SI system) is based on a platinum-iridium weight stored in France. This prototype artifact has been the reference for how much a kilogram should weigh, and has been in use since 1889. Researchers have long wanted to replace this reference prototype with a definition that is based on fundamental constants of nature.
A revised definition will allow scientists and researchers around the world, and even on other planets, to reproduce the kilogram without having to access the reference prototype, and instead depending on universal constants. Planck's Constant, which is a fundamental part of quantum mechanics, relates mass to electromagnetic energy. The constant was first recognised by German theoretical physicist and Nobel laureate Max Planck.
The US based National Institute of Standards and Technology have used a device known as the Kibble Balance to make the most precise measurements of Planck's Constant so far. The measurement is 6.626069934 x 10−34 kg∙m2/s with an uncertainty of thirteen parts per billion. This new measurement will allow for a more precise and universal definition of the kilogram. Accurate measurements of Planck's Constant were a part of a campaign to redefine all SI units on the basis of fundamental constants in nature. The kilogram, along with the other SI units, are scheduled for a redefinition in November 2018.