UTC, English for Universal Time Coordinated as Coordinated Universal Time, has replaced Greenwich Mean Time. It is a combination of the international atomic time TAI and the Universal Time (UT). The 24 time zones are expressed as positive or negative deviation of the UTC.
The allocation of time zones and UTC is relative to the zero meridian in Greenwich, England, which was established at the International Meridian Conference 1884 as a convention.
The UTC is used as the reference time for time values in many areas, so. For example, in aviation and seafaring, in science and in emails or on the Internet generally.
UTC in the world of the mechanical watch
If you find the term "UTC" on a watch, it is equipped with an additional hand, which performs one turn within 24 hours. The primary purpose is to display a second time zone, for example, home time while away from home. The hand can also be used to distinguish between day and night or for orientation, because it indicates the north direction in the northern hemisphere and the south in the southern hemisphere when the normal hours hand is pointed at the sun.
The term UTC is now mostly found on the watches of some progressive and technology-oriented manufacturers, such as Sinn or IWC, while models from other manufacturers because of tradition still carry "GMT" in the name or on the dial, for example the Rolex Oyster Perpetual Date GMT-Master II.