New acquisition!
For those unfamiliar (I know Longines doesn't make frequent appearances here), this is their "world timer", in the Master Collection.
There are many watch mechanisms that tell more than one time zone, and they are typically separated into two categories: the GMT complication, and the world timer complication. The GMT complication is typically represented by a fourth hand that tells the time in another time zone, going around the dial once a day.
The simplified explanation on how that is achieved, is by another wheel in the movement that is coupled to the hour wheel, but with twice the number of teeth, so that it rotates twice as slowly as the hour hand.
It is therefore a mark of genius for Louis Cottier to link that wheel, instead to the 24-hour hand, to a counter-rotating 24-hour
chapter ring. (In reality, the world timer came before the GMT complication.)
The chapter ring moves around the dial once a day, same as the GMT hand, and with an inner bezel showing 24 cities representing different time zones, one could view the time in many locations at a glance.
This world timer complication, however, comes in a few main variations: I'll list the characteristic watch for each variation.
The Patek Phillipe 5230: The latest generation of the original world timer, it includes a pusher for quick local time zone change. The city representing the local time (the 12 hour hand) will be at the top of the dial. Advancing the pusher advances the hour hand (+1), while the city ring advances counter-clockwise with the 24 hour chapter ring. When traveling, just advance the pusher until the city you're in is at 12 o'clock on the dial, and you're set.
The Longines "GMT", as shown above: Instead of Patek's pusher, advancing the local time is done via a quick-set hour hand, similar to the Rolex GMT II. The city disk is static, while the 24 hour ring rotates. One advantage of this is that you don't have the names of cities written upside down, and all the cities will be at the same location on the dial regardless of where you set the local time. So if you're used to NYC at the 8 o'clock position, and you travel to Paris, referencing Eastern Standard Time is still at the 8 o'clock position. The date complication works both ways, if you move the quick-set hour hand from 1am to 11pm, the date goes backwards to accommodate traveling behind to another time zone (e.g. GMT +8 to GMT +5) across the international date line.
The GP 1966 WW.TC: The city ring rotates, but it's not linked to the movement like the Patek. To change the local time, rotate the left crown to set the location (your current location would be at the top of the dial), and change the time in the regular way (no quickset hour), and the 24 hour ring will turn accordingly.
The Hamilton GMT Jazzmaster: The city ring rotates like the GP WW.TC, and it is also not linked to the movement. There is a conventional GMT hand, which you set to a city's time, and rotate the city ring manually to match that city to the GMT hand. This is also the most cumbersome, because you have to set the city ring before reading off the different times.
The Nomos Zurich World Time: Although this has a city ring, it only tells two time zones at a time. You set the pusher to the city of interest, and the local time will be changed (similar in concept to a quick-set hour hand). You have a home time indicator at the 3 o'clock position.
Due to price considerations and the desire to have a date complication on my world timer, the Longines is a perfect fit. The mechanism is also simple, as you only need to quick-set the hour hand for a new location. At 38.5mm, it's sized nicely too. The alligator strap on a deployant clasp is a definite plus at this price range.
The only problem was that this watch has been out of production for a while. I hunted high and low and finally found one in the boutique
