A 24-hour indicator is a dial, subdial or hand that shows time on a scale running to 24 hours instead of the usual 12. The hand turns once a day, so no separate AM/PM indication is needed. Its fans say it removes any doubt about whether a time is morning or afternoon.
How is a 24-hour indicator laid out?
A full 24-hour main dial is one option. Many watches instead put the 24-hour indication on a small subdial, often to show a second time zone. Most 24-hour watches do not number all 24 hours, because that many numbers would crowd the dial. Inside the case, the ETA 2893-2 is said to be the only movement designed to be used as a 24-hour movement.
How does the Explorer II use it?
On the Rolex Explorer II, the 24-hour display uses an extra orange hour hand. It reads against an engraved bezel. Because the hand turns once a day, the wearer can tell daytime hours from night-time hours. That helps where day and night are hard to tell apart, such as in caves or at the poles. The same hand can also show a second time zone.
Where it comes from
The 24-hour dial is far older than the wristwatch. In medieval times, many clocks had 24-hour dials, following the example of the astrolabe. The clockmakers John Harrison, Thomas Tompion and Mudge all made clocks with 24-hour dials. On the wrist, Glycine’s Airman No.1 pilot watch of 1953 is credited as the first watch with a rotating 24-hour bezel. The idea became well known after Rolex created the GMT-Master for Pan Am pilots in 1954. Today, people who work around the clock, such as pilots, nurses, paramedics, police officers and firefighters, commonly use 24-hour clocks and watches.
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