GMT & Second Time Zones

In 1954, Pan Am asked Rolex for a watch that could show its pilots two time zones at once. The answer — the GMT-Master and its extra 24-hour hand — became one of the most useful complications ever made, and the go-to watch for travelers ever since.

Why 24 hours?

The extra hand turns once per day, not twice. Point it at a 24-hour scale and it can say “22:00” instead of an ambiguous “10 o'clock” — you always know whether it's day or night in the other zone before you dial a colleague at 3am. That's also why classic GMT bezels are two-tone (the famous red-and-blue “Pepsi”): one color for daylight hours, one for night.

Using one, in practice

• Regular hands — local time, wherever you are.
• 24-hour hand — home time (or UTC, if you fly planes or ship software).
• Rotating 24-hour bezel — turn it by an offset and the same hand reads a third zone.

On a “true” traveler's GMT, the local hour hand jumps in one-hour steps without stopping the watch — land, click the hour forward, done. On a “caller” GMT (most affordable ones), it's the 24-hour hand that adjusts independently instead. Same dial, different convenience.