Complication · Time zones
Dual Time / GMT
Partially verifiedA complication showing the time in a second time zone in addition to local time, typically via an independently adjustable additional hour hand, a 24-hour hand referencing a rotating or fixed bezel, or a subsidiary dial.
Definition
A complication showing the time in a second time zone in addition to local time, typically via an independently adjustable additional hour hand, a 24-hour hand referencing a rotating or fixed bezel, or a subsidiary dial.
Historical origin
Popularised in wristwatches from the 1950s for airline navigator and pilot use, with the Rolex GMT-Master (introduced 1954) among the best-known early examples designed for Pan American Airways pilots to track a reference time zone alongside local time.
How it works
In the classic GMT-hand design, a fourth hand makes one revolution every 24 hours (rather than 12, like the ordinary hour hand) and reads against a fixed or rotating 24-hour bezel, allowing a second time zone to be tracked without an extra subdial; the 24-hour wheel is geared at half the speed of the ordinary hour wheel.
Many modern GMT designs make the local-time hour hand independently jumpable in one-hour steps via the crown, without stopping the seconds or disturbing the minute hand, so the wearer can quickly adjust for a new local time zone while the 24-hour GMT hand continues to track the reference zone.
Simpler 'dual time' watches instead use a small subsidiary 24-hour or 12-hour dial for the second time zone, driven by its own reduction gearing from the main train and typically adjustable via a secondary crown or pusher.
GMT and Dual Time: A display of a second time zone alongside local time.
An additional hour hand geared to the same train shows a second zone, usually on a 24-hour scale so day and night are distinguished.
In more developed designs the local hour hand jumps independently so the wearer can change zone without stopping the watch.
Pocket watch context
Not a standard historical pocket watch complication; dual-time and GMT functions are essentially aviation-era wristwatch developments and are rare or absent in the antique pocket watch record.
Wristwatch context
A widely produced and commercially important complication, especially valued by frequent travellers and, historically, by airline pilots needing a fixed reference against Greenwich Mean Time.
Identification
- A fourth hand tracking a 24-hour scale on the bezel or dial, or a distinct subsidiary 24-hour dial
- Jumping local-hour-hand mechanisms are a specific refinement worth checking for on GMT-marketed pieces
- A fourth hand reading a 24-hour scale
- A rotatable 24-hour bezel in some designs
Servicing notes
The additional 24-hour drive train and, where present, the independent hour-jump mechanism should be checked for correct synchronisation during service; this is routine but calibre-specific work for a qualified watchmaker.
General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.
Background
The GMT complication serves as a mechanism to display the time of a second time zone. A fourth hand, which functions like a 24-hour watch hand, completes one full rotation every twenty-four hours to indicate the time in this additional zone. The GMT 'desk' variant allows the user to adjust the 24-hour hand independently without affecting the hour or minute hands, usually in one-hour increments.
The GMT 'traveler' variant enables the adjustment of the local hour hand without altering the 24-hour or minute hands. This traveller configuration helps users adapt to local time while maintaining a reference time on the 24-hour hand.
Written from the encyclopedia entries listed under Sources; each statement was checked against the cited text. Passages from sources in other languages are given in English translation.
Construction and action
- Rotating bezels can be used in conjunction with a GMT movement to track a third time zone.
Use and later history
- GMT traveller movements are typically considered more high-end because they are harder to add to existing movements.
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- Complication (horlogerie), Wikipedia (French), retrieved 2026-10-28 (text CC BY-SA 4.0)
- Rolex company history regarding the 1954 GMT-Master, treated as a manufacturer-sourced claim
- de Carle, D., Watch and Clock Encyclopedia
- Britten, F. J., Old Clocks and Watches and Their Makers
- Horological Journal (British Horological Institute), technical articles
Where sources disagree, the disagreement is stated rather than resolved silently.