The New International System of Units: A vision of Max Planck comes true

The discovery of the quantum Hall effect (QHE) revolutionized our international system of units (SI units). High precision measurements of the quantized Hall resistance opened up the way to relate fundamental constants directly to measured quantities. This triggered the introduction of a new international system of units based on constants of nature. The quantized Hall resistance is not only important for electrical standards but also for the realization of the mass unit kilogram.