In today’s world of smartphones and their many available apps, a watch can be more of a fashion statement than something of a functional accessory. However, that doesn’t mean that there isn’t a need or demand for a timepiece with a useful complication. For the watch enthusiast who enjoys traveling the world, a GMT watch would not only be a great accessory for your wrist, but could also be very useful as a functional tool for keeping track of different time zones. This article is going to explain what a GMT watch is and how it’s used.

History of GMT

Greenwich Mean Time (GMT) is the yearly average of the time each day when the Sun crosses the Prime Meridian at the Royal Observatory, Greenwich. The Royal Observatory Greenwich is known world-wide as the home of GMT.

Mean time is clock time, not astronomical time, as astronomical time can vary throughout the course of a year. Greenwich Mean Time is a way of standardizing time so that you can know exactly what time it is, regardless of your location in the world. GMT begins at Midnight and starts over at the next.

During the mid-1600’s, the invention of the pendulum clock made it possible to work out the relationship between mean time and astronomical time. John Flamsteed created the formula and published a set of conversion tables.

By the early 1670’s, he was appointed as the first Astronomer Royal and relocated to the new Royal Observatory in Greenwich. He had the best pendulum clocks installed and set them to the local time, which became Greenwich Mean time. During this time, GMT was really only useful to those who followed astrology.

Railways and How They Popularized GMT

In the UK during the mid-1800’s, the Railways were beginning to discover that they needed a standard to keep track of time as opposed to every station and town having their own. As the railways continued to expand, the need for an international time standard became a must.

In December of 1847, GMT was adopted across Great Britain by the Railway Clearing House as it officially became known as Railway Time. By 1880, Greenwich Meantime became the legal standard for the country and the US had already chosen it as the basis for its own national time zone system.

What is a GMT Watch?

So now that you understand what GMT is and how it came about, we can focus on what a GMT watch is and how it works. Simply put, a GMT watch is equipped with the GMT complication, which will allow you to keep track of two or more separate time zones at once.

Rolex created the first wrist watch in history to feature the GMT complication. Named the GMT Master 6542, it featured a fourth hand, in addition to the 3 original hands; the fourth hand is a second hour hand used to keep track of GMT hours. The bezel of the watch is two toned, red and blue, to indicate AM or PM.

The Original Rolex GMT Master 6542 was developed in collaboration with Pan Am Airways in 1954. The airline company requested a reliable watch that was capable of displaying more than one time zone for use on transatlantic flights. Using the GMT complication, pilots were able to set their watches to a second time zone, which was extremely useful.

How to Use It

A GMT watch features the traditional three-hands, plus a fourth hour hand that follows the 24 GMT hours on the bezel. The bezel has the ability to rotate, which will allow the wearer to set it to any time zone they desire. With the GMT hand being 24 hours, it will only go around the dial once a day.

Remembering that GMT is ground zero for time zones, the wearer can measure the time zone they’re in by how many hours that time zone is away from GMT. Also, understanding military time will be very useful for tracking GMT.

For example, to track local Greenwich Mean Time you would first set the bezel with the 24 hour or triangle mark to the top (above the 12-hour mark on the dial). Say we are in Chicago, IL (GMT -5), we would simply set the GMT hour hand to what the current GMT hour it is.

So, if it’s 5 PM in Chicago, we would move the GMT hand to the 17th hour on the GMT bezel. The dial’s minute and second hand will also count the minutes and seconds for GMT as well. So now our dial’s hour hand is pointing to the number 5 mark, while the GMT hour hand is pointing to 17 (17:00) on the bezel.

Now, let’s say we want to track the time for New York, which is one hour ahead of Chicago. We would leave the hour hand set to the local GMT hour which was at the 17-hour mark on the bezel. Now we would rotate the bezel one click to the left (left means ahead of time, right means behind our time). Now the GMT hand should be pointing at the 18-hour mark, which would indicate that the time is 6:00 PM in NYC.


With advent of smart phones, GMT is easier than ever to figure out, even without the need of a watch or understanding 24-hour time. A simple app could immediately tell you the Greenwich Mean Time for whatever city you’re looking for. However, that doesn’t mean that a GMT watch doesn’t have a place in your collection as they can still fulfill a need of keeping track of two different time zones and, no matter what, they will always look better on your wrist than a handful of glass and plastic.

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bgalo1 · May 1, 2019 at 1:50 AM

Very nice looking site – very informative – I used to love to buy watches, had to stop. thumbs up.

Derek · May 1, 2019 at 2:13 AM

What a tremendous and highly informative article!. We all know what GMT is in terms of time and time zones but not the history and the how it came into common use and relationship to railways!

I actually enjoyed this – thanks!.

Ralph Martin · May 1, 2019 at 10:24 PM

Hey this is a great post! I travel quite a bit and do enter into different time zones quite frequently. This would be very useful to me. Plus I agree, it does look quite nice as well. Keeping track of two different times zones at the same time in addition to having a stylish watch serves several purposes. Thanks again for your post.

    Jerry Strickland · May 2, 2019 at 10:14 PM

    Thanks for reading! I agree, keeping track of two time zones is very useful for someone like you who travels often. Of course your smartphone could do it, but it wouldn’t look as good as a watch!

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