What is a GMT watch?

A wristwatch with a second time zone.

GMT watches have a second hour hand and can therefore display multiple time zones simultaneously. Frequent flyers, globetrotters, and businesspeople especially appreciate the GMT function on a wristwatch, as this complication allows them to read their local and home time at a glance.

The second time zone is displayed by a second hour hand, which is usually arrow-shaped and color-coded. While wristwatches normally measure a 12-hour time interval, with the hour hand completing two revolutions of the dial within 24 hours, the GMT hand completes only one revolution within this time period. The GMT time is usually read via the bezel or rehaut, a raised rim that frames the dial.

GMT / UTC – Two names for the same function

The abbreviation GMT stands for Greenwich Mean Time. Originally, GMT was considered the global standard time to which all local times in the world were to be aligned. This time zone was established at the Meridian Conference in Washington in 1884. GMT is based on measurements of the Earth's rotation – determined on the Earth's prime meridian. This meridian runs from the North Pole to the South Pole and passes through the Old Royal Observatory, located in the London suburb of Greenwich.

The introduction of GMT served to ensure the punctuality of trains and to eliminate inaccuracies in shipping and air traffic. Before the introduction of GMT, station clocks, for example, were set according to the position of the sun. Since this varies from place to place, this sometimes led to very significant delays. The GMT time zone was therefore an indispensable feature until it was aligned with Coordinated Universal Time (UTC) in 1977. UTC is not a time zone itself. It is a time standard, determined using atomic clocks, for calculating local times worldwide. Watch manufacturers use both the terms GMT and UTC to describe a watch with a second time zone. Both functions are identical.

How to use the GMT complication

Using the GMT function is quite simple:
- First, set the GMT hand to your home time.
- Then, set the hour hand to your current local time.
- If your watch has a rotating bezel, you can rotate it to the local time of another location, just like the GMT hand, and thus keep track of a third time zone using the bezel.