Horology & Navigation: All the Different Types of GMT Watch Explained
A GMT watch can be for traveling, navigating, business or keeping track of loved ones abroad. But there are subtle differences in the design of a GMT watch depending on the use-case, but they all look pretty much the same regardless. So with the recent post-covid boom in demand for GMT watches, let’s set out the subtle differences once and for all.
The True GMT of the Jet Age
Greenwich Mean Time (GMT) was first instigated in London in 1884 as what can be thought of as the center of time itself. It is where at 12 noon the sun is at its highest point, in the middle, or meridian. The other places on the globe where 12 noon is denoted as before or after GMT are demarcated by the difference between that place and Greenwich: Paris is GMT plus one hour, Tokyo plus 9, and New York minus 5.
Back in the 19th century, time zones were crossed in sea voyages over weeks, sometimes months. But in 1954, when Pan American Airlines ordered a fleet of Boeing’s new 707 jetliners, that all changed. The Jet Age took flight and pilots needed a way to track the time of their country of origin (home time) and the time of the place they were in (local time) as well as the international standard civil time (GMT).
Rolex famously heeded the call, just as they had done the previous year by creating the Explorer watch for the first successful summit of Mount Everest. They introduced the GMT Master in 1955, a watch who’s bi-directional rotatable 24hr bezel and additional 24hr hand meant Pan Am’ pilots could keep track of GMT, home and local timezones by glancing at the GMT hand or by rotating the bezel.
Three years prior to the release of the GMT Master, Glycine created an aviators’ watch with a 24hr dial and GMT hand to track GMT while flying - the Airman.
These kinds of early GMT watches, namely those for pilots to track GMT specifically, are dubbed ‘true’ or ‘traveller’ GMTs; supposedly because they are for keeping track of actual GMT while flying across time zones, rather than merely keeping track of any other second time-zone. Brands like Rolex, Omega and Grand Seiko stick to producing ‘true’ GMT’s
The Office / Caller GMT
While the earliest GMT watches were intended for pilots or travelers, sometimes one might simply wish to keep track of another time zone than the one they are permanently in. This might be a loved one living abroad or a business partner who you do not wish to accidentally wake in the middle of the night with a phone call (hence ‘caller’). For this use, brands give you the option to independently set the GMT hand to whichever time zone you like, rather than your local hour hand. This way, your watch tells the time for where you are while the GMT hand shows the time of your acquaintance abroad.
This creates a tradition in watch enthusiasm that the traveller GMT, one whose local hour hand is adjustable, is more romantic than the ‘office’ GMT. However, if you were to need a GMT watch to keep track of another country’s time, it would be annoying to have to use the 24hr hand for your local time and independently set the conventional hour hand of your watch for the timezone you aren’t in, so preference really depends on the intended use.
But note, with any GMT watch with a bezel, other timezones can be found by simply moving the bezel accordingly - if you’d like to know the time in New York while you’re in the UK, move the bezel anti-clockwise 5 positions and look at the GMT hand for the time.
To sum up so far, ‘true' or ‘traveller' GMT’s have an independently-set local hour hand, while ‘office’ or ‘caller’ GMT’s have an independently set ‘GMT’ hand.
World-timer vs Flyer
The world-timer and flyer watches, although not strictly a kind of GMT watch on account of the lack of an additional GMT hand, is another confusing nuance.
The world-timer is a time-only watch with an inner rotating bezel which shows different time zones and popular cities within each timezone. One can find the time in Cairo by simply spinning the bezel until Cairo is at 12 o’clock.
The flyer watch, on the other hand, is a world-timer who’s second-timezone uses an additional inner bezel showing the major cities, operated using a pusher or additional crown. The flyer watch can be thought of as a world-timer which actually shows you the second time zone, rather than just giving you a reference with an inner bezel.
Put short, world-timers are technically time-only, while flyers are two-timezone watches with a world-timer bezel/dial.
Notable GMT Innovations
Some watch designs don’t fit into any of the true, traveller, office, caller, flyer or world-timer categories. One such example is the Patek Philippe Aquanaught Travel Time, which with the press of a pusher can advance the hour hand to track local time, leaving behind a skeletonised hand which retains home time.
Another is the IWC Timezoner, which looks like a chunky world-timer, but the local time updates to the time shown on the bezel when you turn it. When flying from London to Paris, moving the bezel clockwise one position will move the hour and GMT hands as well.
Finally, a curious watch from Longines, designed for pilots and using principles of mean time and home time, but isn’t a GMT watch, is the Lindbergh Hour Angle Watch. This watch uses the difference of ‘hour angles’ of GMT and local time to determine longitude, but this is a story for a whole new article.