Coordinated Universal Time is a time scale that couples Greenwich Mean Time, which is based solely on the Earth's inconsistent rotation rate, with highly accurate atomic time. When atomic time and Earth time approach a one second difference, a leap second is calculated into UTC.
UTC was devised on January 1, 1972 and is coordinated in Paris by the International Bureau of Weights and Measures.
UTC, like Greenwich Mean Time, is set at 0 degrees longitude on the prime meridian.
