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.
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
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.
Related photographs
No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.
Sources & references
- Rolex company history regarding the 1954 GMT-Master, treated as a manufacturer-sourced claim
Where sources disagree, the disagreement is stated rather than resolved silently.