Why the GMT is probably the coolest watch complication in the world

Ever wondered why some seemingly “normal” time-only watches have an extra hand?  A hand in a contrasting red color and that moves even slower than the hour hand?  It usually even has an arrow point, right?  And while we’re on the subject, ever wonder why many of these watches have what looks like a dive bezel?  Welcome to the world of the GMT, a type of mechanical wristwatch that displays a second time zone via that red 24-hour hand that goes around the dial once every 24 hours, and a rotating 24-hour bezel, which in conjunction with the 24-hour hand is designed to track a third timezone.


Speaking of Rolex, the first GMT watch was, in fact, created by Rolex in collaboration with Pan American Airways called the GMT-Master way back in 1954.  And in case you were also wondering, the GMT watch (also known as a dual time zone watch) was initially developed for pilots who needed a way to keep track of (at least) a second time zone while flying.  That’s right, time zones a terrestrial reality that even the most travel-challenged of us are acutely aware of especially if you’re based in (for example) Hong Kong but need to contact a colleague in (for example) Switzerland.  But we digress.


A fact that most people have forgotten, however, was that Rolex didn’t create the first watch for pilots that displayed a second time zone.  That honor goes to the Glycine Airman, a watch that is still available today.  It displayed the time in a 24-hour (rather than 12-hour) format, and featured a rotating bezel with 24-hour markings to track a second time zone.  But while the Airman was indeed the first, it was the Rolex that reaped all the glory.

The concept on which the GMT-Master was based, however, dates back even farther than that.  All to way back to 1884, in fact, when Greenwich, England was declared “Mean Time” by international convention, and became the standard against which the rest of the world’s time zones would be compared.  Alas, the time of Greenwich Mean Time (GMT) was not meant to last as it was designed for the era of slow boat travel and the era of Jet-powered air travel would not abide by that.

It didn’t help matters when the atomic clock was invented in 1955, and especially five years later when the US and the UK synced their atomic radio time signals into what would become Coordinated Universal Time, or UTC for short, which has been around since 1967.  This is a more accurate version of Greenwich Mean Time (although this is still used to represent civil time in Britain) and accommodates the timekeeping differences that arise between the aforementioned atomic time and solar time, which is derived from astronomical measurements of the Earth’s rotation on its axis relative to the Sun (this is a protracted subject best saved for another time… pardon the pun).  But, again, we digress.


Over the years, the GMT complication has evolved by leaps and bounds.  Early GMTs, such as the Rolex GMT-Master, were simple beasts with a 24-hour hand anchored to the main hour hand.  This means as you adjusted the local time, the GMT hand moved as well tracking the same local time but on a 24-hour scale making it necessary to rotate the 24-hour bezel to determine the second time zone.  It was only much later when the GMT evolved to a point that either the GMT hand or the main hour hand could be adjusted independently.  Which brings us to…

Despite a modern GMT’s straightforward simplicity, however, most people outside of the traveling community don’t know how to properly use a GMT, much less know that there are actually two types of GMT watches.  The first is what is known as a “Caller” GMT.  This type of GMT is also called an “Office” GMT and is best used by a person in an office who needs to communicate with people in different time zones.  This is made possible by a 24-hour hand that can be set independently of the other hands.  

The recently introduced UNDONE Basecamp Quest Automatic GMT, for example, is a caller GMT.  When its crown is pulled out to its first position, rotating it clockwise allows you to set the GMT hand in 1-hour increments on the 24-hour scale.  Moving the crown out to the second sets the main hour and minute hands, which is followed by the 24-hour GMT hand.


This function is perfect for someone in an office who only has to worry about the time in another timezone.  In other words, the main “home” time displayed by the main hands will most likely hardly ever change, and it’s the time displayed by the 24-hour GMT hand that needs to be adjusted periodically.  Using the example mentioned above, if the user is based in Hong Kong and needs to communicate with someone in Switzerland, the user would set his GMT watch’s 24-hour hand to six hours behind of what the main hour hand is showing.  This way, the time in both Hong Kong (home time) and Switzerland can be seen at a glance.

The second type of GMT watch, called a “Flyer” GMT is the exact opposite.  Unfairly also called a “True” GMT due to the fact that it is the type of GMT favored by pilots, the flyer GMT sees its main hour hand independently set in 1-hour increments and not its 24-hour hand.  This function is incredibly useful for people traveling to different time zones, such as pilots or business executives who need to adjust their watches to a new local time on a daily basis, but need to keep track of “home” time displayed by the 24-hour GMT hand.  An independent main hour hand that can be independently set in 1-hour increments satisfies this requirement.


We have yet to explain how to use the 24-hour bezel to track a third time zone, or how pilots actually set their GMT watches (that’s right, many of them set their GMTs differently from “civilians”).  But those can be tackled at another time.  In the mean time, here you have it: a beginners guide to the GMT.  If you are based at home but need to communicate with a colleague at the other side of the world, a “Caller” GMT is what is called for.  But if you are a frequent traveller visiting multiple destinations with different local times, then a “Flyer” GMT is best for you.  Just make sure to research on the movement functionality of the GMT watch you plan to buy to determine the type of GMT it is.  

Unlike other more “complicated” watches, the functionality of the GMT makes it inherently useful in real world situations.  And with the advent of modern technology that gives you immediate access to every corner of the globe and its people, this makes the seventy-year-old GMT the coolest mechanical complication out there.