Coordinated Universal Time (), abbreviated as UTC, is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time (GMT). For most purposes, UTC is considered interchangeable with GMT, but GMT is no longer precisely defined by the scientific community. UTC was officially formalized in 1960 by the International Radio Consultative Committee in Recommendation 374, having been initiated by several national time laboratories. The system was adjusted several times until leap seconds were adopted in 1972 to simplify future adjustments. A number of proposals have been made to replace UTC with a new system that would eliminate leap seconds but no consensus has yet been reached. The current version of UTC is defined by International Telecommunications Union Recommendation (ITU-R TF.460-6), Standard-frequency and time-signal emissions and is based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the slowing of Earth’s rotation. Leap seconds keep UTC within 0.9 second of universal time, UT1. See the “Current number of leap seconds” section for the number of leap seconds inserted to date.
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