The time zones were standardized in the 19th century in order to maintain the schedules for the train systems. The current system consists of 24 standard meridians of longitude beginning in Greenwich, England. GMT stands for Greenwich Mean Time and is the starting point for the 24 time zones.Continue Reading
Locate your current location as a starting point.
From your current time zone on the map, count over to the GMT.
Add 1 hour for each time zone that you counted to the east. Subtract 1 hour for each time zone that you counted to the west.