What does “GMT” mean?

A GMT watch shows a second time zone, usually with an extra hand that goes around the dial once every 24 hours, read against a 24-hour scale on the bezel or dial. GMT stands for Greenwich Mean Time. With a rotating 24-hour bezel, many GMT watches can track a third time zone as well. Rolex's GMT-Master, developed in the 1950s with airline crews in mind, is the most famous example.

There are two main types. On a 'flyer' or 'true' GMT, the local hour hand jumps independently, so travellers can change time zone without stopping the watch; on a 'caller' or 'office' GMT, the 24-hour hand is the one set independently. Modern Rolex GMT-Master II models are the first type. Buyers care about the difference, so dealers state it and test that every setting function works correctly before selling.

Example: 'True GMT with jumping local hour hand, all functions working.'