Developing a new balance for the new kilogram

In the coming year the kilogram will be revolutionized as the original kilogram -- a 4 cm small cylinder made from platinum and iridium having been stored under three glass domes in a safe near Paris since 1889 -- is becoming lighter. Within one hundred years it has lost 50 millionths of a gram. As all scales worldwide refer indirectly to this unique kilogram, they all weigh incorrectly even if it is only minimal and negligible. Although the original kilogram is becoming lighter, structurally identical copies of the prototype remain constant worldwide -- which means, as the original kilogram is the measure of all things, these copies are slowly becoming heavier. Therefore, a new standard is required which does not change and cannot be damaged or lost.

In 2018 the new "kilogram" will be adopted at the 26th General Conference on Weights and Measures -- a kilogram that is not defined by an object or a physical mass, but by a physical constant: the Planck's constant. The highly precise continuously measuring Planck balance, developed by the German university Technische Universität Ilmenau, operates on the principle of electromagnetic force compensation. Simply put, a weight on the one side is to be balanced by electrical force on the other. This electrical force is inextricably linked with the Planck's constant and can be directly referred to the new kilogram definition. As this balance is the first self-calibrating instrument of its kind, masses determined as reference or standard masses for calibrating scales and balances are no longer required. Another advantage of the Planck balance is its wide measuring range covering a range from milligrams to one kilogram. At the end of the year the first prototype of the balance will be available and ready for use.