GMT refers to a watch complication that displays a second time zone, typically using a 24-hour format, allowing the wearer to track time in two different locations simultaneously.
Set your local time normally, then adjust the GMT hand to your home timezone or second timezone using the crown's additional position. The 24-hour GMT hand completes one rotation per day, allowing you to track two timezones simultaneously.
A GMT watch tracks two timezones using a 24-hour hand and rotating bezel. A world time (worldtimer) watch displays all 24 timezones simultaneously using a city disc or multiple subdials, making it easier to read multiple timezones at once.
GMT stands for Greenwich Mean Time, the time standard based on the Royal Observatory in Greenwich, London. The complication was originally developed for pilots who needed to track both local time and GMT for international navigation and flight coordination.