The GMT function for wristwatches was originally developed in the 1950s for pilots. Their job regularly took them back and forth between different time zones, so they needed a timepiece that did not constantly have to be set to the new local time. The acronym GMT refers to Greenwich Mean Time: the official ‘world time’ until 1928. Today it has been replaced by UTC or Coordinated Universal Time, however most watchmakers still use the older terminology when referring to watches with a second time zone. How do GMT watches work? Two hour hands show the time at your place of origin and your destination simultaneously. The additional hour hand is not read via the dial with its 12 hourly markers, but rather using the exterior ring or bezel, which has a 24-hour marking. So you read the time either ‘inside’ or ‘outside’ the dial, depending on the time you wish to know.