Natural units are a system of measurement used in physics. In natural units, only universal physical constants are used as defining constants. This means that each of these constants acts as a coherent unit of a quantity. Natural units are used principally in particle physics. The system sets fundamental physical constants, such as the speed of light and the charge of an electron, equal to 1, which eliminates the need for conversion factors and simplifies equations. ^{wikipedia.org 1 2 3 4}