As something of a nerd for travel watches, I can’t help but obsess over the myriad permutations that exist within the basic concept of a watch that shows the time in two (or more) places. I am also routinely surprised by how often I cross paths with someone who doesn’t know how to get the full functionality from their travel watch. Predictably, this happens most commonly with the most common form of the travel watch, the GMT.

Largely popularized by the Rolex GMT-Master and GMT-Master II models, a standard GMT can come in a few flavors, but the core functionality is tied to the presence of both a 24-hour hand and a rotating 24-hour bezel. The movement in use can be a flyer (local-jumping hour) or a caller (independent 24-hour hand), but the ability to track the additional timezone is derived from the additional 24-hour hand, and the ability to do even more comes from being able to rotate the 24-hour bezel.

Is the following guide going to be both reductive and also somewhat pedantic? You better believe it. But you might just thank me the next time you need to change the indicated 2nd timezone on your GMT because you’ll be able to do so without so much as touching the crown or moving any of the hands.

Most of the time that I see someone using a GMT, they have it set like a traditional “dual time” watch, where the local time is displayed on the main hands, and the 24-hour hand shows the time in a second time zone by reading the bezel in its default position (shown below, with zero-hour at logical 12 o’clock position on the dial). While this is fine, and indeed is the feature set provided by any fixed-bezel “GMT” (actually a dual time) like a Rolex Explorer II, it doesn’t harness all that your 24-hour GMT is capable of – to get the most out of the watch, you need to use the bezel.