What is a GMT watch and how does it work?

The GMT function is a very useful complication, especially for those who travel frequently, as it allows quick reference to both the time of the place being visited and the time of the place of origin.

What does GMT time mean?

GMT means Greenwich Mean Time. This might be interpreted as your watch showing the time of the Greenwich meridian, but it is not; a GMT watch allows multiple time zones (2 or more) on a single watch dial.

HOW CAN YOU TELL IF A WATCH IS A GMT?

GMT watches usually have two hour hands indicating the time, and this GMT hand is often red. 
Some watches have a time scale on the bezel or within the dial itself.
The second time zone consists of a second hand that rotates around a 24-hour dial.

HOW TO USE THE GMT FUNCTION?

The dial of standard wristwatches generally measures a 12-hour time interval. This means the hour hand makes two full rotations around the dial within 24 hours. To indicate GMT, the watch has an additional hour hand, typically arrow-shaped and a different color from the 12-hour hand. Unlike the hour hand, the GMT hand takes 24 hours to complete a full rotation around the dial, so its speed is half that of the other hand. The GMT time is read through the 24-hour bezel.

Besides their aesthetic appeal, GMT watches are especially practical for those who travel abroad. Thus, a person traveling from Frankfurt to Sydney will have to continuously remember that the time difference compared to local German time is 8 hours and, therefore, when arriving in Australia, will always have to calculate the time based on German time. This becomes even more complicated if that person also has relatives in New York. In this way, a GMT watch will help avoid these types of problems very easily.

But let's see concretely with this example how to use the GMT function on a watch that separately includes an adjustable hour hand.

You can set the different time zones at any time, whether still at home or once landed in Sydney at 8:00 PM. You simply need to set the GMT hands on the dial to European time (12:00). Then, also adjust the hour hand to Sydney local time (8:00 PM). To set New York time, move the 24-hour bezel (GMT hand) to the corresponding time of that city (6:00). With these brief and simple steps, you will now have three time zones simultaneously.

HOW DID GMT WATCHES ORIGINATE?

As the Earth rotates around the Sun, the light it receives shifts, and although this fact is now considered established, until the mid-19th century it was unknown, and there was no awareness of time changes worldwide.
Only in Germany, each of the principalities had its own time. Over time and with the arrival of railways, the existence of so many time zones caused chaos since more than 30 different time zones had to be considered.
In 1884, after endless negotiations, an agreement was reached to divide the Earth into 24 time zones and the Greenwich meridian, GMT, was established as the “zero” hour.
In the 1960s, this was replaced by UTC, Universal Time Coordinated, whose main feature is the use of dividing the day into 24 hours based on time zones.
The GMT format was invented in watchmaking so that travelers could quickly know the time anywhere in the world. These watches became rapidly popular in the aviation world, as they were able to show pilots the time of the origin and destination locations.
24-hour based GMT watches are widely used in navigation and communication protocols to avoid confusion.

WHY DO YOU NEED A GMT WATCH?

Nowadays, the possibility of traveling has been made easier, and thanks to the GMT function of the watch, you can know the time in different countries.
It is important to remember that the watch must be set, and in this way, with just a glance, you can know the time in different parts of the world.