This video will explain how to use the GMT function on a watch. A GMT watch is sometimes also called a dual time watch since it displays two time zones at once. In its most basic form, a GMT watch has the traditional 12-hour hand to show the local time, in addition to a 24-hour hand that points to a 24-hour scale to indicate another time zone.
Rolex introduced the GMT-Master watch in the 1950s explicitly for Pan Am pilots to track two time zones. During this era, Greenwich Mean Time or GMT was a time standard used by civil aviation. Therefore, the Rolex GMT-Master watch allowed pilots to read GMT via the 24-hour hand pointing to the 24-hour marked bezel and local time on the dial via the main hour hand. Today, Coordinated Universal Time or UTC is the standard reference time.
On the original Rolex GMT-Master watches, the 24-hour hand was coupled to the main hour hand. That means that when you set the time, all the hands move together. When the bezel is in the neutral position, which is when the upside down triangle is positioned at 12 o’clock, the main hour hand and the 24-hand tell the same time. So, to use this type of GMT watch, you have to turn the bezel to align the correct numeral with the 24-hour hand to display another time zone. Now you can read the local time on the dial and another second time zone on the bezel.
In the 1980s, Rolex introduced the GMT-Master II model where the main hour hand could now be set independently from the 24-hour hand. So, to use this type of GMT watch, first make sure the bezel is in the neutral position. Then, unscrew the winding crown and pull it out to the last position. Turn the winding crown, which moves all the hands together. Keep turning the crown until the 24-hour hand points to the number on the bezel of the reference time zone. Then adjust the minute hand to the correct time. Push the crown one notch in. Now you can “jump” the hour hand to display local time when you turn the winding crown. If you need to adjust the date, keep moving the hour hand forward past midnight until the correct date appears in the window. Set the hour hand to the correct local time. Push the crown in all the way and screw it back into position. Now you can read local time on the dial and reference time on the bezel. You can also read a third time zone by turning the bezel by the correct number of offsets in relation to reference time.
Whenever possible, always refer to the official manufacturer’s instruction manual for more details on how to use your specific GMT watch model.