What is a GMT?

Before a unified time system was established, each city had its own local time. At one point in the United States, there were over 100 different local times. In those days, it was extra challenging for travelers to keep track of time. There were very few options for a two time zone watch. Double-time pocket watches tracked both local and railway time, and captain watches displayed local and homeport time. However, most travelers carried several watches to track time on their journey.

The ability to travel increased exponentially during the industrial revolution. It was then that the world took note of the importance of a more unified time system. In 1884, representatives from over twenty countries gathered in Washington D.C. for the International Meridian Conference. Here, they established the Greenwich meridian to have a longitude of zero degrees and divided the globe into 24 time zones, each one hour apart. These time zones were based upon GMT, also known as Greenwich Meridian Time or Greenwich Mean Time.

While you may not know the history of the Greenwich meridian, perhaps you’ve heard of a GMT watch. Maybe you’re still wondering, what is a GMT watch? Watches with a GMT function allow the wearer to tell the time in multiple time zones. Learn more about GMT, Dual Time, and World Time at Crown & Caliber.

The world’s first GMT-Master, the ref. 6542, had a novel way to tell the time in two different locations at once. The now-iconic “Pepsi” watch had a dual red-and-blue color scheme, a rotating 24-hour bezel, and a red 24-hour hand. While many GMT watches made today are made by other brands, the GMT-Master was a unique and advanced technological innovation in its time.

Since their creation, GMT watches have risen in popularity not only for their functionality but also for their aesthetic appeal.  Undoubtedly, the GMT watch has evolved greatly over the years, varying in its look as well as function. They have also remained very relevant today due to the increased globalization. And while they may not be as visually arresting as world timer watches, plenty of companies have made the GMT function all their own.

Precursor to the GMT: The World Timer

It wasn’t until the 1930s that a watchmaker translated the new global time system into a timepiece. Watchmaker Louis Cottier was the first to develop a world timer for brands like Rolex, Patek Philippe, and Vacheron Constantin. His concept featured a traditional watch face in the center of the dial, displaying local time. He coupled this with a rotating 24-hour ring surrounded by the names of different cities. Cottier’s design continues to serve as the base for modern world timers.

Today, we know there are in fact 37 time zones in our world map. It hasn’t been until recent years that a watchmaker created a world timer that accounts for each. In 2011, Vacheron Constantin debuted the first wristwatch to tell time in all 37 time zones: the Patrimony World Time. Soon after, Glashütte Original developed their own versions, first with the Grande Cosmopolite Tourbillon and then the Senator Cosmopolite.

What Is a GMT Watch?

The aviation boom of the 1950s sparked the development of two time zone watch and subsequently the GMT. Much like railway operators and ship captains needed to track time in multiple cities, pilots faced the same challenge. They needed a device that could tell time in their current city and their destination. The GMT function helped solve the pilot’s problem. Rolex was the first to pioneer a dual time zone watch. In 1954, they collaborated with Pan Am to develop the GMT Master. 

The world’s first GMT-Master, the Reference 6542, had a novel way to tell the time in two different locations at once. The now-iconic “Pepsi” watch had a dual red-and-blue color scheme, a rotating 24-hour bezel, and a red 24-hour hand. While many other brands make GMT watches today, the GMT-Master was a unique and advanced technological innovation for its time.

Since their creation, GMT watches have risen in popularity not only for their functionality but also for their aesthetic appeal. Undoubtedly, the GMT watch has evolved greatly over the years, varying in its look as well as function. Today, they continue to remain relevant due to ever-increasing globalization. While they may not be as visually arresting as world timers, GMTs come in many forms as companies find ways to make them all their own. 

How to Spot a GMT Watch

Despite the many takes on this type of timepiece, a few features remain consistent among true GMT watches. Watches with a GMT function use a 24-hour scale to indicate the second time zone. They’re typically comprised of a 24-hour track along the bezel or outside of the dial. This may be fixed or rotating. Then, a fourth hand indicates the second time zone along the 24-hour scale. In addition, most GMT watches feature a setting crown with three positions to operate all the functions.

Dual Time Watches

Another example of a two time zone watch is the dual timer. The Dual time watch emerged around the same time as watches with a GMT function. They essentially perform the same function. However, they do so through different mechanisms. A dual time watch displays two time zones simultaneously with a main dial and subdial. Some modern examples of the dual time watch include the Patek Philippe Nautilus Travel Time Chronograph and Jaeger-LeCoultre Grande Reverso Duoface.

Picking the Best Timer for Your Needs

Are you a pilot or do you only tend to travel from your home to a single city? If so, a dual time watch or GMT may be the most practical option for you. A dual time watch is more straightforward and user-friendly, while GMTs can take a little more finesse to operate. Instead, are you an avid traveler, often visiting multiple destinations on a single journey? Then nothing quite compares to the capabilities of the world timer.

Editor’s Note: This article was originally published on May 15, 2015. We have updated it for clarity.

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Image Credits: Header,2-3; Crown & Caliber. 1; World Time Zone.