The Chamorro Time Zone, formerly the Guam Time Zone, is a United States time zone which observes standard time ten hours ahead of Coordinated Universal Time (UTC+10:00). The clock time in this zone is based on the mean solar time of the 150th meridian east of the Greenwich Observatory. The zone includes the U.S. territories of Guam and the Northern Mariana Islands, where the Chamorro people are the original inhabitants. Since Daylight Saving Time (DST) is not observed anywhere in this zone, the time is always known as Chamorro Standard Time (ChST).