GMT / Dual Time — The Traveler's Essential

A GMT or dual-time watch lets you read two or even three time zones at once, which is why it has been the traveler's and pilot's companion since the jet age began. Home and away, all on one dial, without ever losing track of where you are.

Why do travelers need a second time zone?

When you cross time zones, keeping one hand set to home time and another to local time solves real problems: knowing when it is polite to call family, catching a connecting flight scheduled in a different zone, or simply staying oriented after a long flight. The complication was popularized in the 1950s when transatlantic air travel took off and pilots and passengers needed to track multiple zones reliably, and it has been a staple of pilot and travel watches ever since.

GMT versus dual time versus world timer

• GMT: an additional hand makes one full rotation every 24 hours and points to a 24-hour scale, usually on the bezel or a ring, showing a second zone
• Dual time: a separate sub-dial, often with its own small hour and minute hands or a 24-hour indicator, displays the second zone independently
• World timer: a rotating 24-hour ring paired with a ring of city names shows the time in all 24 zones simultaneously, at a glance

How does a GMT hand work?

The GMT hand tracks a 24-hour cycle rather than 12, so it can distinguish day from night in the second zone. You read it against a 24-hour scale: if the GMT hand points to 18 on that scale, it is 6 PM in the tracked zone. A two-tone bezel, like the famous red-and-blue "Pepsi," visually splits day from night to make that even easier to read. The clever part on the best travel GMTs is how you adjust it.

Caller versus flyer: two kinds of GMT

• Caller GMT (or office GMT): the independent GMT hand is set separately, ideal for someone who stays home and wants to track a distant colleague or family member
• Flyer GMT (or true GMT): the local hour hand jumps in one-hour steps independently of the minutes and the GMT hand, so when you land you simply push the hour hand to local time without stopping the watch, and home time keeps reading correctly on the GMT hand

The flyer style is what frequent travelers prize, because you can reset to a new zone in seconds without disturbing the running seconds or the minutes.

Iconic GMT watches

• Rolex GMT-Master II "Pepsi" — the definitive travel watch, developed with Pan Am pilots and named for its red-and-blue day/night bezel
• Tudor Black Bay GMT — a robust, well-priced Swiss GMT with a true traveler's movement
• Grand Seiko SBGE257 — a Spring Drive GMT pairing smooth timekeeping with a second zone
• Rolex Explorer II — a GMT with a fixed 24-hour bezel, born for cavers who lose track of day and night

How to set and identify a GMT

To use one, first set the GMT hand and main hands together to home time against the 24-hour scale, then rotate the bezel or jump the local hand to display wherever you have traveled. The clearest sign you are looking at a GMT is that extra, often brightly colored, hand sweeping a 24-hour track, or a two-color day/night bezel. Since it can be hard to tell a flyer GMT from a caller GMT, or a true GMT from a plain 24-hour display, the AI Watch Identifier app can identify the model from a photo and tell you which type of dual-time system it uses, so you know exactly how to reset it before your next flight.