Most of the time zones in the world are based on “Coordinated Universal Time” (UTC, international time standard). However, the earth’s rotation is not as regular and is minimally smaller than was defined when this time standard was defined. For this reason, so-called “leap seconds” are inserted into the UTC time scale from time to time. Since the natural rotation of the earth is not perfectly constant, the insertion of leap seconds is done as needed and according to no fixed pattern. Leap seconds are determined in such a case by the International Earth Rotation and Reference Service (IERS). However, the responsible state institution is usually responsible for the official time of a particular country.