World clock

A world clock is a clock which displays the time for various cities around the world. The display can take various forms:

• The clock face can incorporate multiple round analogue clocks with moving hands or multiple digital clocks with numeric readouts, with each clock being labelled with the name of a major city or time zone in the world. The World Clock in Alexanderplatz displays 146 cities in all 24 time zones on its head.[2][3]
• It could also be a picture map of the world with embedded analog or digital time-displays.
• A moving circular map of the world, rotating inside a stationary 24-hour dial ring. Alternatively, the disc can be stationary and the ring moving.
• Light projection onto a map representing daytime, used in the Geochron, a brand of a particular form of world clock.

The Weltzeituhr (World Clock) at Alexanderplatz in Berlin[1]

There are also worldtime watches, both wrist watches and pocket watches. Sometime manufacturers of timekeepers erroneously apply the worldtime label to instruments that merely indicate time for two or a few time zones, but the term should be used only for timepieces that indicate time for all major time zones of the globe.