====== Dual timezone ======

A **dual timezone** is an additional display feature or [[complication]] of a watch.

===== Definition =====

{{wst>image_cl|A. Lange & Söhne|Lange 1 Zeitzone Rotgold (2020)|A. Lange & Söhne Lange 1 Time Zone, with a **second timezone** display at 5:00}}

Dual timezone watches can display both [[local time]] and the time in another time zone. 

One popular use for this feature is known as [[GMT]], in which a watch displays both local time and Greenwich Mean time **on a 24 hour scale**, a feature useful for pilots. GMT is a subset of dual timezone, however, that must have a 24 hour scale or [[day/night indicator]] for "home time". Some dual timezone watches lack the 24 hour scale and simply have a second hour hand. Others have useful complications for travelers rather than pilots, including airport codes (as on the [[Nomos Tangomat GMT]]), a globe, and so on. For example, the [[Jaeger-LeCoultre Reverso Duoface]] has pushbutton adjustment for the rear dial, with the intention that a traveler will leave the front face at their "home" time and use the pushbutton to adjust the rear face as they travel.

Another related complication is the so-called [[worldtimer]] watch, which displays the time in many timezones at once. Many of these use the same dual timezone movement as a simple dual-time watch but include a disc in the face showing timezones around the world along with day and night indicators.

Some watches have a [[24 hour]] hand or subdial that is locked to the main dial and are therefore not dual timezone or GMT watches.

===== History =====
{{wst>image_cl|Rolex|GMT-Master II|[[Rolex GMT-Master II]]\\ with the additional feature of a dual time-zone (green hand)}}

The need for such models arose as air traffic became more popular in the [[1940]]s and [[1950]]s, when more and more flights lead through several time zones. Thus the [[Rolex GMT-Master]], one of the classics of this watches genre, was developed in [[1954]] by [[Rolex]] as a result of specific requests from pilots to track GMT along with local time. The GMT-Master has a long hour hand that makes one revolution around the dial in 24 hours and points to a [[bezel]] marked with 24 hour increments as well as a short hour hand that can be moved to follow local time. This format (two central hour hands, one of which has a 24 hour scale and the other which can be independently set on a 12 hour scale) is known as a "true GMT".

As travelers began purchasing GMT watches, they often set the "base" time to their home timezone rather than GMT. This led to the development of traveler-friendly complications like [[worldtimer]]s. Since many such watches are not set to GMT, watches with extra 12-hour independent hour hands began appearing.

===== See also =====
  * {{tagpage>Dual_timezone_watches|Dual timezone watches}}
  * [[Duo dial]]
  * [[Dual movement]]
  * [[GMT]]
  * [[Worldtimer]]


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