The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time (UTC−8). The standard time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC−7 and is thus based on the mean solar time of the 105th meridian west of the Greenwich Observatory. The largest city in the Pacific Time Zone is Los Angeles; the city's metropolitan area is the largest in the zone.