It’s Complicated: GMT/Dual Time/World Time

In this edition of “It’s Complicated” we are discussing what I think is one of the most useful watch complications, even in today’s smartphone-driven world; the ability to tell the time in two different places at once.  There are 3 different types of complications that fundamentally serve this purpose; the dual time, the GMT, and the World time.  I will get into all three shortly, but first a bit about why we need this complication in the first place.

A Brief History of Time(zones)

Today time zones seem like just a fact of life.  One that can irritate any watch lover driving through Indiana, but otherwise not something anyone thinks about too much.  However before the advent of modern time zones most towns set their clocks buy the sun, meaning that every place with a clock had a slightly different time (most closely aligned with solar mean time).  In the 1800s the US alone had over 300 different timezones.  This made any form of standardized travel challenging and risky (in a future post we will go into more detail on the effects this had on the railroads in the US).  What changed the timing game was the creation of the chronometer.  As highly accurate marine chronometers became more common on ships in the 1800s their accuracy made it possible to create a timing standard based on mechanics that would deviate very little (and thus be reliable for navigation and scheduling).  Timekeepers now needed to decide what that standard should be, so they held a conference.  In 1884 in Washington DC the International Meridian conference met to decide the fate of time itself (pause for dramatic effect).  They settled on the Royal Observatory in Greenwich England as their time standard because at the much of the worlds shipping passed through England and the Greenwich Observatory had a reputation for reliable timekeeping.  And thus Greenwich Mean Time was born.  Today, with atomic clocks accurate to 1 seconds every billion or so years there is a new time standard called UTC (Universal time coordinated), but GMT has stuck as a reference to the basis for time zones and in modern watchmaking language.  Looking back its pretty incredible to think about the implications of this decision made by a relatively small group of men 130 years ago.  Everything from the standard appearance of maps to the phrase “GMT” derives from this decision to set the Prime Meridian as passing through Greenwich. Okay, enough of a history lesson for now, back to the watches.

An image of the Royal Observatory from 1898, you can see why they took Greenwich “mean” time, look at all those chronometers.

GMT Watches

Since we just got done discussing the birth of the concept of GMT, this seems like a good place to start.  GMT watches were originally developed for Pilots as a way to track both local (or home) time and GMT, which they used for all radio communications and flight tracking.  A GMT watch has standard hour and minute hands then has a third hand, usually part of the central hand stack but sometimes in a subdial, that rotates once around the face every 24 hours.  In older GMT watches the GMT hand was anchored to the hour hand so a rotating bezel was necessary to indicate GMT vs home time.  In most if not all modern GMT watches the GMT hand can now move independently of the other hands, allowing the wearer to set it to any alternate timezone.  A GMT watch is arguably the most pure expression of a second timezone and a complication with real roots in tool watches of the past.  It is also a very accessible complication, with Hamilton producing beautiful GMT watches right alongside Rolex and the other luxury brands.



Dual Time Watches

The simplified version of a GMT watch is the dual time watch.  A dual time watch is very similar to a GMT watch except the additional hand goes around the dial once every 12 hours instead of every 24 hours (hence Dual time instead of GMT).  This is less traditional, but more practical for the everyday wearer.  Many dual time watches will also have a quick set button that allows the wearer to advance the hour hand in hour increments by just pressing a button.  This is extremely helpful for those who travel a lot or those, like me, who are clumsy with a watch crown and may accidentally change the time instead of adjusting the second hour hand.  For whatever reason these seem to be less common then traditional GMT watches, despite their practicality, but their are some great options out there.  Again the simplicity of this complication, both in appearance and in mechanical construction, makes it relatively accessible in the world of watches.  That said, its popularity with the jet-set class means that the Pateks and Langes of the world also offer beautifully made dual time watches. The simplicity of a dual time function also breeds creativity among watchmakers.  While adding a second hour hand of a slightly different style or color is an easy way of achieving a beautiful and effective dual time watch, many brands such as Breguet and Laurent Ferrier have chosen to use dial windows and other display methods to achieve the same function.  My favorite dual time display method, though, has to be Jaeger Le Coultre’s Reverso Duo.  Why adjust a single hand when you can flip your watch around and have a whole new watch?

The JLC Reverso Duo- Two watches for the price of one, relatively speaking

World time watches

Finally we have what might be considered the haute horology version of the GMT watch, the world timer.  World timers usually use a disk with 24 hour markers along the outside of the home time dial.  Outside of that disk there is a fixed disk that indicates the names of cities in each of the different time zones around the world.  The hour disk rotates once every 24 hours such that you can see the current time in each of the listed cities at any time of day.  Still following?  It can be difficult to follow, but the result of actual use is much simpler.  Say you want to know the time in London, simply find London (or a nearby city) on the outer dial and then look at the 24 hour dial to see the time, simple.  The World timer has historically been the real of high end watchmakers.  The first serially produced world time watch was from Patek Philippe and it remains in production and one of the most recognizable (and in my opinion beautiful) world time watches being produced.  Today though brands like Longines and Brietling are producing beautiful World Timers at much more reasonable prices.  What would make you purchase a world time watch instead of the other more simple and often less expensive second time zone options?  The big advantage of a world timer is that at a glance you can see the time basically anywhere in the world (except those weird places with non-standard time zones).  If you have work colleagues around the world on one conference call I can see how this could be very useful, but for personal use a dual time watch remains the most practical option.

Longines and Patek world time watches, the same, yet so different


A watch’s fundamental function is to tell the time, so its a pretty logical expansion of that purpose for a watch to be able to tell the time in more than one place.  Displaying two time zones at a glance may also be the one place a watch may still be able to beat the Iphone in your pocket (although I’m sure there is an app for that). A second time zone is a massively practical complication that is so simple it gives watchmakers the opportunity to be creative and take something basic and make it interesting. If I were building a watch collection from scratch a dual time watch would be right at the top of my list, and in fact I have the very Hamilton GMT above in my own collection (I’m sure it will make an appearance in the Owners Experience series soon). Watches tell the time, watches are tools, and the GMT/Dual time/World timer complication is a lasting vestige of that character.




2 thoughts on “It’s Complicated: GMT/Dual Time/World Time

  1. wms1228

    Good point, I don’t particularly like the distinction between false/true GMT watches. The function is fundamentally the same, the “true GMT” label is for the purists out there who are most focused on the implications of the complication as opposed to its use. Thanks for reading!



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