To use a GMT watch, read the extra hand against the 24-hour scale: it shows the hour in a second time zone, in 24-hour form, so you can tell day from night. Set that hand to your home time and the ordinary hands to the time where you are. If the bezel rotates, turning it lets you read a third time zone without touching the crown. How you set the watch depends on which of the two kinds of GMT movement it has, and it is worth knowing which you own.
A GMT is one of the most useful complications for anyone who travels or works with people abroad. This guide explains how to set and read one.
The parts of a GMT watch
A GMT watch has everything an ordinary watch has, plus two things:
- The GMT hand. A fourth hand, usually with an arrow or triangle at its tip and often in a contrasting color. It goes round the dial once every 24 hours, half the speed of the hour hand.
- A 24-hour scale. Numbered from 1 or 2 up to 24, either on the bezel or on a ring around the edge of the dial.
The GMT hand points to the hour on the 24-hour scale. If it points to 15, it is 3 p.m. in that time zone; if it points to 3, it is 3 a.m. There is never any doubt about morning or evening, which is the whole point when you are about to telephone someone on another continent.
The name comes from Greenwich Mean Time, the reference time that pilots and navigators used. The first watch of this kind, the Rolex GMT-Master of 1955, was made for airline crews.
Two kinds of GMT: which do you have?
This is the part most guides skip, and it changes how you set the watch.
The traveler's GMT
Pull the crown out to the middle position and turn it: the ordinary hour hand jumps forward or backward in one-hour steps. The minute and seconds hands keep going and the watch does not stop. The GMT hand stays where it is.
This type is made for people who travel. On landing, you click the hour hand to the new local time and the GMT hand goes on showing home. The date follows the local hour hand, forward or backward.
Watches of this kind include the Rolex GMT-Master II, the Tudor Black Bay GMT, the Longines Spirit Zulu Time, and Grand Seiko's GMT models.
The caller's GMT
Pull the crown to the middle position and turn it: the GMT hand moves in one-hour steps, while the main hands stay put.
This type suits people who stay at home and track somewhere else: an office abroad, a family member overseas. Changing the second time zone is quick. Changing your local time when you travel means resetting the main time, which stops the watch.
Many GMT watches at lower prices work this way, because the common Swiss and Japanese GMT movements are built like this.
To find out which you have: pull the crown to the middle position and turn it. Whichever hand jumps tells you the type.
How to set a traveler's GMT
- Unscrew the crown if it screws down, and pull it out fully. The seconds hand stops.
- Set the GMT hand first. Turn the crown until the GMT hand and the minute hand show your home time on the 24-hour scale. The hour hand will move too; ignore it for now.
- Push the crown in one step, to the middle position.
- Set the local hour. Turn the crown to jump the hour hand to the time where you are. Watch the date: as the hour hand passes midnight the date changes, so make sure you are on the right side of noon.
- Push the crown in and screw it down.
When you travel, repeat only steps 3 to 5. Flying from New York to London, you jump the hour hand forward five hours. The GMT hand still shows New York.
How to set a caller's GMT
- Pull the crown out fully and set the main time, as on any watch.
- Push it in one step, to the middle position.
- Turn the crown one way to move the GMT hand in one-hour steps to the second time zone. Turning it the other way usually changes the date.
- Push the crown in.
How to read a third time zone with the bezel
If your watch has a rotating 24-hour bezel, you can read a third time zone, or change the second one in a moment, without using the crown.
The rule: turn the bezel by the number of hours' difference.
Suppose the GMT hand shows home time, New York, and you want to know the time in Tokyo, which is 13 or 14 hours ahead depending on the season. Turn the bezel so that the scale shifts by that many hours against the GMT hand, and read the hand against the bezel. To go back, return the triangle on the bezel to 12 o'clock.
In practice, most owners use it more simply. They leave the GMT hand on home time, and when they want another city's time for a call, they rotate the bezel by the difference and read it off.
A watch with a fixed 24-hour scale, such as the Rolex Explorer II, shows two time zones only.
Reading day and night
Many GMT bezels are in two colors, one for the daytime hours, roughly 6 to 18, and one for the night. That is the reason for the red and blue of the original GMT-Master, and for the blue and black, green and black and other pairs that followed. A glance at which color the GMT hand is over tells you whether it is day or night at home. Our comparison of the Rolex Pepsi, Batman and Sprite covers those bezels.
Common mistakes
- Setting the GMT hand to the 12-hour time. If it is 3 p.m. at home, the GMT hand belongs on 15, not on 3.
- Forgetting the date. On a traveler's GMT the date follows the local hour hand, including backward. After setting, check that the date changes at midnight and not at noon.
- Leaving the bezel turned. If the times look wrong, check that the bezel's triangle is back at 12.
- Forgetting daylight saving. The difference between two cities changes when one of them moves its clocks and the other does not.
- Not screwing the crown down afterward, on a watch that has a screw-down crown.
Other uses
- A 24-hour display at home. Set the GMT hand to the same time as the main hands and it shows you at a glance whether a time on your watch is a.m. or p.m.
- UTC. Pilots, sailors and radio operators set the GMT hand to Coordinated Universal Time, the world's reference time.
Choosing a GMT watch
If you travel often, a traveler's GMT is worth seeking out. If you track one other time zone from home, either type serves. Our guide to the best GMT watches compares the options at each price, and these comparisons go deeper:
- Tudor Black Bay GMT vs Rolex GMT-Master II
- Rolex GMT-Master II buying guide
- Rolex Explorer vs Explorer II
You can browse the Rolex GMT-Master II and Longines Spirit watches we have in stock, or search for "GMT" to see every model.
Frequently asked questions
What does GMT mean on a watch?
It stands for Greenwich Mean Time. A GMT watch has an extra hand that shows a second time zone on a 24-hour scale.
How do I read the GMT hand?
Read where it points on the 24-hour scale. 15 means 3 p.m.; 3 means 3 a.m.
How do I set the second time zone on a Rolex GMT-Master II?
Set the GMT hand to home time with the crown fully out, then push the crown in one step and jump the hour hand to local time.
What is the difference between a traveler's GMT and a caller's GMT?
On a traveler's GMT the main hour hand jumps in one-hour steps, which suits changing time zones. On a caller's GMT the 24-hour hand is adjusted instead, which suits tracking another place from home.
Can a GMT watch show three time zones?
Yes, if it has a rotating 24-hour bezel. Turning the bezel by the time difference gives a third zone.
Why is the GMT bezel two colors?
To separate day from night in the second time zone: one color for the daytime hours and another for the night.
