The times in the various time zones are based on Universal Coordinated Time (UTC). UTC has taken over the function of Greenwich Mean Time (GMT). UTC and GMT are both aligned to the zero degree of longitude, which runs through Greenwich, London. The times in the other zones are calculated by adding or subtracting mostly whole hours, depending on the distance from the prime meridian. In a few countries, such as Iran, Afghanistan, India and certain areas of Australia, there are also time differences to UTC of 3½, 4½, 5½ or 9½ hours.