How to read the second time zone
Set the 24-hour hand to the reference zone and read it against a 24-hour scale, which may be printed on the dial or bezel. The ordinary 12-hour hand shows another time. A rotating 24-hour bezel can add a third zone by changing the reference scale, though the method varies by design.
Because the 24-hour indication distinguishes day from night, it is useful for avoiding an accidental call at 3 a.m. in another city. When setting a GMT watch, verify the displayed date and whether the 24-hour hand is linked to the minute hand or to another setting control.
Caller GMT versus traveler GMT
In a caller-style arrangement, the independent 24-hour hand is typically adjusted to the second zone, while the local hour hand remains tied to the main time-setting mechanism. This can be convenient for checking a remote time from home.
In a traveler-style arrangement, the local hour hand jumps in one-hour increments, making it convenient to change local time after landing without stopping the movement. These labels are common shorthand, not a universal guarantee; manufacturers may describe calibers differently. Read the manual for the exact reference.
GMT, UTC and the name
GMT originally refers to Greenwich Mean Time and is often used colloquially for a second-time-zone watch. UTC is the modern time standard used as a reference in many technical contexts. For everyday travel, a watch's 24-hour display can be set to a chosen zone, whether or not that zone is formally called GMT.
Choose based on how you will set it: frequent travel favors an easy local-hour adjustment, while monitoring a fixed home time may make a caller-style setting perfectly suitable. Check crown positions, date behavior and quick-set instructions before use.