Watches pictured above (Seiko SBDB001/ Omega flightmaster 911/ RXW MM25/ Rolex 16570 Explorer II)
An interesting (and popular) mechanical watch complication is the GMT hand. It allows one to follow multiple time zones at a glance. It works in the following way: the “regular” hour hand shows the local time. The GMT hand, on the other hand, points to another time zone. Since most time zones are whole numbers (e.g. +/- 1, +/- 2), it is easy to calculate the time in other parts of the world by simple addition/subtraction. As an example, say you live in NY and plan on traveling to Paris: To prepare for your trip, you would first set the GMT hand to the former time zone – say 20:00 (most GMT setups use 24 hour military time). Once you arrive in Paris, you would adjust your hour hand to the local time there. Now you can easily follow time in two different parts of the world. There are different mechanisms that allow for this, some of which are easier to use than others. The following is a summary of the crown operated types.
The Rolex Way
In my opinion, the most ideal is the “Rolex” version. It allows you to change the (local time) hour hand without having to stop (hack) the watch. Moreover, you can adjust the hour hand both forwards and backwards. The drawback is that it is not as easy to change the date – you have to advance the hour hand by 2 full rotations to do that – the quick set date is sacrificed for this complication. The model shown is a 16570 Explorer II, which uses the tried and true 3185 caliber movement. It’s important to mention that the Grand Seiko automatics and Spring Drives also function this way.
The Omega flightmaster Way
Another option is limited to the (older) Omega 910/911 flightmasters. These watches have a dedicated crown for the blue hour (local time) hand and it can be positioned anywhere (clockwise only though.) This is unlike the “Rolex” version, which can only jump in fixed one-hour intervals. It is an extremely flexible system, but is limited to these to vintage models.
The ETA 2893 Way
The third option is a modified ETA 2893. In this case, you can only move the GMT (not local time) hand in one direction. Rotating the crown the other way will change the date. A consequence of this is that you have to stop the watch in order to move the (local time) hand. Due to price considerations, this is the most common version you will see on the market.
When possible, it is best to seek out a watch with an independently adjustable local time hand. Once you get used to the convenience of not having to hack (stop) your watch for travel/daylight savings changes, it becomes really hard to go back to the other way. Objectively, it should not really matter if the ETA movement will require another 30- 60 seconds of adjustments. Subjectively, it feels oddly jarring and crude. I can’t believe I actually wrote that, but there it is :). Also, if you need to track oddball time zones, the flightmaster is one of the few mechanicals that would have you covered. Please keep in mind that there are also push button GMT setups available, but they are more obscure and (IMHO), unnecessarily complex.
Below is a video demonstrating these movements in action.