16.09.2024
GMT watches and GMT function
explained clearly
GMT watches are not only popular with frequent flyers and globetrotters, but also with people who work a lot with colleagues in other time zones. But what does GMT actually mean and how did the GMT function come to be built into watches? What are the features of a GMT watch? How do you set the second and third time zones on the different types of GMT watches and how do you read the times? This article aims to answer all these questions.
GMT time
Meaning and history
GMT stands for "Greenwich Mean Time". This refers to the division of time zones that representatives from 25 nations agreed on as a reference for world time at the International Meridian Conference in Washington in 1884. Up to this point, each country and sometimes even individual regions had their own time, which was based on the highest position of the sun and announced by the respective church towers or station clocks. This worked quite well until technical progress, particularly in the field of rail transport and telegraphy, led to the desire for a uniform time or uniform time zones. The solution was the introduction of a worldwide standard time to which everyone could orient themselves. At the International Meridian Conference in 1884, Greenwich Mean Time (GMT) was chosen. 24 of the 25 country representatives voted in favor of the Greenwich meridian as the official prime meridian. The fact that the Greenwich meridian was chosen also had to do with the fact that this meridian was already used in shipping. In 1972, GMT time was replaced by Coordinated Universal Time (UTC) as world time.
The GMT function
In addition to the classic 12-hour dial, GMT watches typically have a bezel with a 24-hour display and an additional GMT hour hand. Depending on the type of GMT watch, this allows a second or even third time zone to be set.
The watches were originally developed for aviation so that pilots could see two different time zones at a glance. As GMT time was regarded as world time at the beginning of aviation, this designation was simply adopted for this type of watch and has not been changed since. the interaction between the GMT hand and GMT bezel is crucial for the GMT function. For this reason, these two components will be examined in more detail first.
GMT hand
The GMT hand is an additional hour hand that stands out visually from the rest of the hands due to its size and usually striking color and can be moved independently or depending on the type of GMT watch. Unlike the normal hour hand, the GMT hand takes 24 hours to circle the dial of the watch once.
GMT bezel
In addition to the GMT hand, the GMT bezel also plays an important role in watches with a GMT function. The GMT bezel can be used to set the second or third time zone. Like the GMT hand, the GMT bezel displays 24 hours and is usually two-colored to distinguish between day and night. Unlike the diving watch bezel, the GMT bezel can usually be turned in both directions.
Setting a GMT watch correctly
To set a GMT watch correctly, you first need to know what type of GMT watch you actually have. There are two different types of watches with a GMT function: first-generation GMT watches, in which the hour and GMT hands can only be moved simultaneously, and second-generation GMT watches, in which the hour and GMT hands can be moved independently of each other. Second-generation GMT watches can be further divided into office GMT or caller GMT and true GMT or traveller GMT.
Setting first-generation GMT watches
In the first generation of GMT watches, the GMT hand and the hour hand cannot be moved independently of each other as they are linked. This means that whenever you move the hour hand, the GMT hand also moves at the same time. It is important to understand that the hour hand moves at 12-hour intervals and the GMT hand, as already mentioned, at 24-hour intervals.
If you want to use the GMT function to display a second time zone on a first-generation GMT watch, you first set the hour hand to show the local time. For the second time zone, the 24-hour GMT bezel is then aligned with the GMT hand so that the hand points to the corresponding number on the bezel that corresponds to the time in the desired time zone;
This means, for example, that when it is 8 p.m. (winter time) in Germany, it is 2 p.m. in New York. The GMT hand is at the 10 o'clock position on the first generation GMT watches. To display New York time, the bezel is now turned until the GMT hand points to the 14 o'clock mark on the bezel.
Setting second-generation GMT watches
In contrast to the first generation, the GMT hand and the hour hand can be moved independently of each other on second-generation GMT watches.
As already mentioned above, there are two different types:
- Office-GMT and Caller-GMT. Caller-GMT, in which a foreign time zone is usually displayed with the GMT hand, and
- True-GMT or Traveller-GMT, in which the GMT hand usually displays the home time.
Setting the Caller GMT or Office GMT
With the Office GMT, the GMT hand can be set forwards by turning the crown in the second position and - if the watch has a date display - the date can be changed by turning the crown in the other direction. This does not change the local time, which is very practical; in the third position of the crown, all the hands move together. To set a second time zone, only the GMT hand needs to be aligned with the bezel.
If you also want to set a third time zone, you also align the GMT bezel with the GMT hand, just as with the first-generation GMT watches. In this case, the second time zone must be based on the hours shown on the dial and multiplied by two, as the GMT hand needs 24 hours to go around the dial and not just 12 like the normal hour hand. Some GMT watches, such as the Circula AquaSport GMT, make it easier to read a third time zone by having an additional 24-hour display on the dial.
Setting the true GMT or traveler GMT
With the traveler GMT, the hour hand for the local time can be set in both directions by turning the crown in the second position, while the GMT hand does not move.
In the third position of the crown, all hands move together, so to set the new local time after arriving in a different time zone, you only need to set the hour hand for the local time, while the GMT hand, which indicates the home time, does not move. With an additional third time zone, the GMT bezel is aligned with the GMT hand, as with the other two GMT watch types.
So if you land in New York at 2 pm, you set the hour hand to 2 pm with the second crown position, while the GMT hand remains at 8 pm (Germany). To additionally display the time in Beijing, you can also adjust the bezel of this GMT watch type so that the GMT hand points to 3 o'clock.
Office-GMT vs. True-GMT
As the names of the two types of GMT watches and the descriptions suggest, the Office-GMT is better suited to displaying the time in another time zone with the GMT hand, while the Traveller-GMT is better suited to keeping an eye on your home time with the GMT hand when you are traveling.
The reasons for this are simple: if you have a traveler GMT, even though you are actually mainly in your home time zone, the GMT hand moves with you every time you set the time (third position of the crown). This means that you first have to set the watch so that the GMT hand is at the desired position and only then can you set the hour hand accordingly. It is exactly the opposite with the Office GMT when travelling: As only the GMT hand can be moved separately here, you first have to adjust all the hands when traveling (third position of the crown) to set the local time and then the GMT hand has to be set to the home time again (second position of the crown).
The Traveller GMT is therefore more practical when traveling, as you can simply adjust the hour hand with the 2nd crown position to set the local time while the GMT hand remains unchanged for the home time. In the office, it is exactly the opposite. The office GMT is more suitable here, as the GMT hand can be set separately with the second crown position and the local time does not change.
Circula AquaSport
with GMT function
The Circula AquaSport GMT is a classic office GMT. It is the perfect choice for anyone who spends most of their time in their own time zone and maintains contacts in other time zones. In addition to the bezel, the GMT watch from Circula has an additional 24-hour scale on the dial so that the different times can be read at a glance even in a third time zone! Instead of the Sellita SW200-1 movement used in the AquaSport II diver's watch, the Circula AquaSport GMT uses the top-of-the-range Sellita SW330-2 movement. This special top-of-the-range GMT caliber is based on the ETA 2892-A2 and enables a second time zone display by means of a centrally positioned GMT hand.
Unlike the unidirectional rotating bezel of the AquaSport II diver's watch, the sapphire crystal bezel of the AquaSport GMT can be turned in both directions. The bezel has a 48-position graduation and the indices are filled with Swiss Super-LumiNova® BGW9.
The other specifications of the Circula AquaSport GMT correspond to those of the Circula AquaSport II:
- Slightly domed, scratch-resistant sapphire crystal with double anti-reflective coating on the inside
- Hands and indexes filled with Swiss Super-LumiNova® C3 X1
- 200 meters water-resistant, screw-down crown (luminous)
- 40 mm diameter, 46 mm horn to horn and 12.6 mm height.
