What are GMT watches and how do they work?
A GMT watch is a watch that offers the simultaneous reading of, at least, two time zones. Alongside local time, it adds a second indication intended to track the time of another city or country with a direct and precise reading.
In practice, it lets you check that additional reference without calculations in your head and with an important advantage, the information is presented in 24-hour format, which makes it easier to identify whether, in that location, it is daytime or night-time.
The term “GMT” comes from Greenwich Mean Time, historically associated with the Greenwich meridian. In watchmaking, “GMT” is used as the usual name for this type of watch function, that is, the ability to show a second time zone, although the modern time-reference standard is UTC.
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Origin of GMT watches
The GMT function developed from the need to synchronise times between regions, a challenge that gained relevance with international time standardisation and the use of Greenwich as a reference. Its consolidation came in the 20th century with long-haul aviation, crews and operators had to work with a stable reference time for planning and communications, without losing the local time at the destination.
That requirement favoured readability solutions, especially the 24-hour indication to avoid misinterpretations. By tradition and widespread use, “GMT” is still today the usual name for one of the most sought-after functions, due to its practical usefulness and clear reading.
Elements that make up a GMT
Local time is shown by the hour hand and the minute hand. The distinctive feature is an additional hand, the GMT hand, which is often differentiated by design or colour. This hand is read against a 24-hour scale, placed on an inner ring of the dial or on the bezel, depending on each model’s layout.
Function of a GMT watch
The GMT hand is calibrated to complete one full rotation every 24 hours, while the conventional hour hand completes two rotations a day. This difference makes it possible to read the second time zone on a 0–24 scale and remove the typical ambiguity of the 12-hour format. If the GMT hand points to “6”, it indicates 06:00; if it points to “18”, it indicates 18:00. The result is an immediate check of the second time zone, especially useful when there is a large time difference or when you need to confirm precisely the time of day in another location.
There are two common architectures, with implications for use. In so-called traveller GMTs (also known as flyer), the local hour hand is adjusted in one-hour jumps without stopping the watch, the GMT hand remains fixed as “home time”, and the date usually changes coherently when crossing midnight.
In office GMTs (caller), what is adjusted independently is usually the GMT hand, and the main time remains as the reference. For frequent travel, the first system is usually more convenient, for remote tracking from a single city, the second may be sufficient.
This type of watch is aimed, above all, at people who need to control times operationally: frequent travellers, executives and international profiles, aviation and navigation professionals, logistics and transport, diplomatic staff, distributed teams and anyone who works with clients or markets in other time zones. It is also common among users who, without a professional obligation, want a useful and legible complication.
In terms of specific uses, a GMT allows you to organise calls and meetings without calculations, keep track of your home country’s time while travelling, coordinate shifts with teams on other continents, monitor market closes or operating windows, and avoid errors with time differences and date changes. If the model allows a third time zone via the bezel, an additional “reference time” can be added (for example, a key office or UTC) to simplify planning even further.
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