What Is a GMT Watch? A Simple Guide to Tracking Two Time Zones
What Is a GMT Watch? A Simple Guide to Tracking Two Time Zones
By Brian Costello, Co-Founder of Seaborne Trading Company
A GMT watch sounds more complicated than it really is.
At its core, it does one simple thing:
It lets you keep track of more than one time zone on the same watch.
That can be useful if you're traveling, working with people overseas, keeping tabs on family somewhere else — or simply wondering what time it is at a place you'd rather be.
Which, admittedly, is how we tend to think about it at Seaborne.
GMT Watches at a Glance
GMT stands for: Greenwich Mean Time
Main purpose: Tracking a second time zone
How it works: An additional hand points to a 24-hour scale
Typical hands: Hour, minute, seconds, plus a GMT hand
Can some GMT watches track three time zones? Yes, when paired with an adjustable 24-hour bezel
Seaborne's GMT: The WaveCatcher GMT uses the automatic TMI NH34 movement
What Does GMT Stand For?
GMT stands for Greenwich Mean Time, named for the Royal Observatory in Greenwich, England.
Greenwich became the reference point for the world's time zones, with the Prime Meridian designated as zero degrees longitude.
You do not need to know any of that to use a GMT watch.
But that's where the name comes from.
In watch terminology, “GMT” generally refers to a watch capable of displaying an additional time zone through a separate 24-hour hand.
How Does a GMT Watch Work?
A normal analog watch has an hour hand that makes two trips around the dial every 24 hours.
A GMT watch adds another hand that typically makes one full rotation every 24 hours.
Instead of reading that hand against the normal 12-hour markers, you read it against a 24-hour scale.
So if the GMT hand is pointing to 18, that means:
18:00 — or 6:00 PM.
The 24-hour scale also solves an obvious problem.
If someone tells you it is 7:00 in another country, you need to know whether they mean 7:00 in the morning or 7:00 at night.
A GMT hand makes that distinction immediately.
Movement maker TMI describes the GMT function in essentially the same way: an additional hour hand rotates once every 24 hours, allowing another time zone to be displayed on the same watch.
Why Would You Want a GMT Watch?
The original appeal is obvious:
Travel.
Imagine you're in California but live in Boston.
Your normal hour and minute hands can show local California time while the GMT hand tracks the time back home.
That way, you can quickly see whether it's a reasonable time to call someone — or whether they're going to be especially unhappy to hear from you.
But travel isn't the only reason GMT watches are useful.
You might track:
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A family member living overseas
-
A company office in another country
-
A client in another time zone
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The time at home while you're traveling
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A destination you're about to visit
Or, in our case:
A surf break on the other side of the world.
More on that in a minute.
Why Does a GMT Watch Use 24-Hour Time?
Because a second 12-hour scale would leave one fairly important question unanswered:
AM or PM?
A GMT hand uses a 24-hour scale so you know immediately whether the second time zone is in the morning or evening.
For example:
08 = 8:00 AM
14 = 2:00 PM
20 = 8:00 PM
Once you get used to reading 24-hour time, it becomes surprisingly intuitive.
And unlike learning to use most complicated watch functions, you probably won't need an instruction manual every time you come back to it.
Can a GMT Watch Track Three Time Zones?
Some can.
If the watch has both a GMT hand and a rotating 24-hour bezel, the bezel can be offset to display another time zone.
That means:
Main hands: Local time
GMT hand: Second time zone
Rotating bezel + GMT hand: Potential third time zone
Citizen, for example, documents this type of three-region use on GMT models equipped with rotating bezels.
Do most people actually need to know the time in three places simultaneously?
Probably not.
But neither has necessity ever been the only reason people like watches.
What Is the Difference Between a GMT Hand and a Regular Hour Hand?
The regular hour hand circles the dial twice per day.
The GMT hand circles it once per day.
That slower movement allows the GMT hand to correspond with a 24-hour scale rather than the standard 12-hour dial.
On many watches, the GMT hand is also deliberately made a different color or shape so it is easy to distinguish from the normal hour and minute hands.
That's not just decoration.
It lets you glance at the watch and quickly separate local time from the additional time zone.
Caller GMT vs. Flyer GMT: Is One Really Better?
Spend enough time around watch enthusiasts and you'll eventually hear two terms:
Caller GMT and Flyer GMT.
You may also hear a flyer GMT described as a “true GMT.”
We don't particularly love that term.
Both are real GMT watches. They simply allow you to adjust different hands independently.
With a Flyer GMT, sometimes called a Traveler GMT, the regular local hour hand can be moved forward or backward independently. That's extremely convenient for someone who frequently flies between time zones. Land in Los Angeles, jump the local hour hand back three hours, and the GMT hand can continue showing your home time.
With a Caller GMT, sometimes called an Office GMT, the 24-hour GMT hand is the independently adjustable hand. Your regular hour and minute hands stay on local time while you move the GMT hand to whichever second time zone you want to follow.
That's the system used by the TMI NH34 automatic movement inside the Seaborne WaveCatcher GMT.
And for what we designed the WaveCatcher to do, we actually think that makes a lot of sense.
Why We Chose a Caller GMT for the WaveCatcher
A Flyer GMT is exceptionally useful if you're constantly getting off airplanes and changing your local time.
But that isn't really the idea behind the WaveCatcher.
The WaveCatcher is built around another use of GMT:
You're here. You want to know what time it is there.
Maybe “there” is home while you're traveling.
But maybe it's Pipeline.
Cloudbreak.
Rincon.
Or somewhere else you're thinking about going.
With a Caller GMT, your normal hands continue showing the time where you are. The GMT hand can then be independently moved to the time zone you want to keep track of.
For the way we imagined people using the WaveCatcher — keeping one eye on local time and another on some faraway place — that's exactly the functionality we wanted.
Is a Flyer GMT better for someone who crosses time zones every week?
It very well might be.
Is it automatically a “better” GMT?
We don't think so.
It's a different tool optimized for a different job.
For a watch inspired by the idea of sitting at your desk and wondering what time it is at Cloudbreak, we'll happily take the Caller.
What GMT Movement Does the Seaborne WaveCatcher Use?
The Seaborne WaveCatcher GMT uses the TMI NH34 automatic mechanical GMT movement.
TMI specifies the NH34 with:
A center GMT hand
Hours, minutes and seconds
Date display
24 jewels
21,600 vibrations per hour
Hacking seconds
The movement is part of TMI's NH mechanical family.
The NH34 uses an independently adjustable GMT hand, making it straightforward to set a second time zone while leaving the main local time display in place.
It is also automatic, meaning the movement is mechanically powered and winds through the motion of your wrist rather than using a battery.
Why We Made the WaveCatcher GMT Different
When we started designing the WaveCatcher, there was one part of a conventional GMT watch that didn't feel particularly Seaborne:
The cities.
Traditional GMT and world-time watches often reference major international cities.
London.
New York.
Tokyo.
Paris.
Perfectly useful places.
But we kept thinking:
What if the watch pointed somewhere you'd rather be?
So instead of filling the WaveCatcher bezel with traditional city names, we used famous surf destinations.
Pipeline.
Cloudbreak.
Maverick's.
Supertubes.
Montañita.
Sultans.
Places associated with waves, travel and being somewhere considerably more interesting than your conference room.
And that's really the idea behind the WaveCatcher.
A GMT Doesn't Have to Be About Business Travel
Historically, the GMT watch makes perfect sense as a travel tool.
Pilots.
International travelers.
People moving between time zones.
But watches don't have to be purely practical.
Sometimes the second time zone can simply connect you with somewhere else.
Maybe you're sitting in Massachusetts and wondering what time it is in Fiji.
Maybe you're headed to Puerto Rico next month.
Maybe your son lives in California.
Maybe you're planning a trip you've talked about taking for ten years.
Or maybe setting the GMT hand to Hawaii while there's snow outside just makes February slightly more tolerable.
We think all of those are legitimate uses.
GMT Watches and the Seaborne Idea
One of the things we like about watches is that they can carry meaning beyond telling the time.
A scratch can remind you of a trip.
A faded strap can remind you of a summer.
A second time zone can remind you of somewhere — or someone — far away.
That's what made the GMT complication interesting to us.
It isn't just about knowing another time.
It's about maintaining a small connection to another place.
And that's very close to the idea behind Seaborne itself:
Some places stay with you long after you've left.
Carry Your Adventure.
Frequently Asked Questions About GMT Watches
What does GMT mean on a watch?
GMT stands for Greenwich Mean Time. On a watch, GMT generally refers to the ability to display an additional time zone using a separate hand and a 24-hour scale.
How many time zones can a GMT watch show?
Most GMT watches can easily display two time zones. Watches with an adjustable 24-hour bezel can sometimes be used to track a third.
Why does a GMT watch have four hands?
A typical GMT watch has normal hour, minute and seconds hands plus an additional GMT hand. The GMT hand rotates once every 24 hours and is used to display another time zone.
What is the 24-hour bezel on a GMT watch for?
The 24-hour scale allows the GMT hand to distinguish between morning and evening. An adjustable 24-hour bezel can also allow some GMT watches to display an additional time zone.
Is a GMT watch useful if I don't travel often?
Yes. A GMT watch can be used to track family, friends, offices or events in another time zone. It can also simply keep you connected to a favorite destination or somewhere you're planning to visit.
What is the difference between a traveler GMT and a caller GMT?
A traveler GMT generally allows the main local hour hand to be adjusted independently, which is convenient when changing time zones. A caller GMT generally allows the GMT hand to be independently adjusted, making it convenient for tracking another location while staying in your home time zone.
Is the Seaborne WaveCatcher GMT automatic?
Yes. The WaveCatcher uses the TMI NH34 automatic mechanical GMT movement, which includes a center GMT hand, date display and 24 jewels.
What makes the Seaborne WaveCatcher GMT different?
Instead of using conventional world-city references, the WaveCatcher bezel highlights famous surf destinations including Pipeline, Cloudbreak, Maverick's, Supertubes, Montañita and Sultans. The idea is simple: use the GMT complication not only to track another time zone, but to keep somewhere you'd rather be a little closer.
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