GMT Watches
Clockwork in the Spotlight: Discover What Makes GMT Watches Unique
With Bucherer and Ariel Adams, discover what makes GMT watches so special, learn about the mechanism behind their complication and find out what the GMT feature on watches means.
We want to start by clearing up a few brief, basic questions before taking a closer look at the topic of GMT watches. To do so, we asked internationally renowned watch expert Ariel Adams to join us for an interview, where he answered a few key questions about GMT watches.
What is a GMT watch?
“In simple terms, a GMT watch is a timepiece with a 24-hour hand that displays a second time zone, in addition to the hands showing the hours, minutes and seconds. It’s not a watch with more than one 12-hour-format dial, as so many people wrongly assume. A GMT watch always has a 24-hour scale that can be adjusted individually so the GMT hand displays a second time zone.”
What does GMT mean in terms of watches?
“‘GMT’ stands for ‘Greenwich Mean Time’, describing the time at the prime meridian, which runs through Greenwich. While scientists tend to use UTC (Universal Time Coordinated), as this shows the atomic time that is precise down to a millisecond, UTC is equivalent to GMT when it comes to the time displayed. This ‘zero hour’ can be used to determine the time anywhere in the world by either adding or subtracting hours to or from it. If you move eastwards from England, you add one hour onto GMT for every new time zone. If you move westwards, you subtract one hour from GMT.”
What are GMT watches used for?
“Nowadays, GMT watches are used by anyone wanting to see the time at two different places in the world on the same watch. This feature of GMT watches makes them perfect for people who do a lot of travelling and always want to know what time it is back at home. Originally, GMT watches were developed for pilots, with one of the most popular GMT watches of all time being the ‘Rolex GMT-Master’ from the mid-1950s. Rolex produced this model with a striking blue and red bezel for pilots at the airline Pan Am. The bezel’s colouring led most people to dub the watch ‘Pepsi’ or the ‘Pepsi bezel’. Rolex invented the GMT watch and was the first company to manufacture it.
GMT watches can have additional complications, too. Breitling’s in-house ‘Chronomat B01 Chronograph 42’ has both a GMT hand and a chronograph.”
GMT watches and movement: special features
With a GMT watch, the wearer is not only able to see the time in their current location, but also a second time/the time in a second time zone. To this end, GMT watches have an additional hand that moves independently of the others.
A GMT movement is more complex and more sophisticated than its standard counterpart: extra components and mechanisms are required so that more than one time zone can be displayed. While a non-GMT movement only needs hour, minute and second hands, additional components in a GMT movement regulate the additional hand that depicts the second time zone in 24-hour format on a special scale or bezel on the edge of the watch face. Specifically, the GMT movement needs to be designed so the wearer of the watch can move the additional hand without impacting the main hour hand. To achieve this, the inner workings of every GMT watch contain two power systems: one regulates the hour, minute and second hands, while the other deals with the GMT hand. This latter hand is driven by an extra cog which rotates at half the speed of that for the hour hand. This cog is simply integrated into the existing movement.
As a result, the GMT hand takes precisely 24 hours for one complete rotation, while the hour hand covers the same distance in half as much time. This special feature and the 24-hour display on the edge of the dial makes it possible for two different time zones to be shown in parallel.
GMT watches need to be calibrated with precision so they can fulfil their brief. This calibration ensures that the GMT hand requires exactly 24 hours for one complete rotation, while the hour hand requires exactly 12. This high level of complexity makes GMT watches a masterful example of precision engineering and a significant advance in watchmaking technology.
Are all GMT watches automatic?
Bucherer offers a wide range of automatic GMT watches, such as those found in Breitling’s Chronomat collection or Carl F. Bucherer’s Patravi line. However, GMT watches do not always have to be automatic. The GMT feature can be integrated into watches with an automatic or hand-wound movement, automatic watches and quartz watches. The feature itself is not dependent on a watch’s drive mechanism and can, theoretically, be used in any model. The “Rolex GMT-Master II” is an example of a mechanical watch with a GMT feature. This is the revamped version of the famous “Rolex GMT-Master” and features a GMT hand and rotating bezel.
Can you also get GMT diving watches?
The GMT watch was initially designed as a pilot’s watch. Now, various watches with a GMT feature are available from an array of renowned watchmakers. Some of them are indeed suitable for use as diving watches, which require the casing to be completely water-resistant. The Tudor Black Bay GMT is one such watch and is water-resistant to up to 20 ATM. It is crucial that the crown is closed carefully after the GMT time has been adjusted: this is the only way to ensure that the watch is indeed water-resistant.
Setting and reading GMT watches
Normally, you can set the GMT hand via the watch’s crown. Here’s how:
- First, turn the crown and pull it out to the second position to adjust all the hands, including the GMT hand.
- Now, you can set the time back home on the GMT watch: simply turn the crown until the GMT hand and the minute hand are showing the current time. The second hand will remain stationary during this.
- Once you’ve set the right time, carefully push the crown back into the first position to set the hour.
- Now, turn the crown until the hour hand is displaying the current local time. If your watch has a date display, make sure this is adjusted too when the crown is in the first position.
- Once you’ve done all this and set the date, hour, minute and GMT time correctly, you can screw the crown back down.
- If you’re now travelling to a different time zone, you simply need to repeat the steps to set hour hand. To do so, unscrew the crown and put it in position 1. This enables you to adjust the hour hand without moving the other hands. In other words, you don’t need to worry that your GMT watch will need re-adjusting every time you change time zone – the second and minute hands will continue to tick round while you’re setting the hour. By extension, this ensures that your watch will run properly once it’s been set.
Now, your GMT watch has been set so you can see two time zones at once: the hour hand shows the current local time, while the GMT hand shows the time in your home time zone.
GMT watches with a rotating bezel offer an alternative way to set the second time: rotate the bezel so 24 is at the top. On most GMT watches, this is depicted as an upside-down triangle. You can now rotate the bezel to instantly set any time zone you like, without needing to unscrew the crown. To do so, turn the bezel until your desired additional time is in the same position as the GMT hand. GMT watches with dual-coloured bezels are particularly sophisticated and convenient. These bezels are a different colour between the numbers of 6 and 18, usually with a lighter half and a darker half. This enables the wearer to see at a glance which numbers relate to daytime and which to night. Rolex, Tudor, Norqain and TAG HEUER, for instance, make watches with a rotating, dual-coloured bezel.
