The original kilogram used to calibrate scales worldwide is a 4-cm cylinder made from platinum and iridium. 
Image credit: Technische Universität IlmenauStored in a safe near Paris since 1889, the kilogram has lost 50 millionths of a gram over the last century. Although the original kilogram is becoming lighter, structurally identical copies of the prototype are used; these copies are slowly becoming heavier relative to the prototype. Therefore, a new standard is required that 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. A Planck balance for measuring the redefined kilogram is under development by researchers from Technische Universität Ilmenau and the National Metrology Institute of Germany. The balance will be used to calibrate other scales or balances so that those correspond to the system with this new method as required. The instrument is also to be used in industry for measuring weights.
The Planck balance operates on the principle of electromagnetic force compensation. A weight on one side is to be balanced by electrical force on the other. 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 is its wide measuring 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.
