World-Time Clocks

Movement & mechanism

• A standard going train drives the hour hand and, additionally, a slowly rotating twenty-four-hour city ring or globe once every twenty-four hours
• Time zone information is presented either as a rotating ring of named cities read against a fixed twenty-four-hour scale, or as a rotating globe beneath a fixed time ring
• Some examples incorporate a day/night indicator ring shaded to show which zones are currently in daylight

Identification

• A ring of city or country names surrounding, or set within, the main dial is the defining visual feature
• A twenty-four-hour (rather than twelve-hour) scale is typically used for the time-zone ring, even where the main dial remains twelve-hour
• Presence of a shaded day/night sector is common on more elaborate examples

Terminology

• Standard time zones — the system of longitudinal time bands, generally dated to international agreements of the 1880s, which world-time clocks are designed to display
• City ring — the rotating or fixed band of place names used to read local time in each zone

Known variations

• Fixed-city-ring, rotating-hour-ring world-time clocks
• Rotating-globe world-time clocks
• Wristwatch-derived world-time complications adapted to clock form

Collecting notes

World-time clocks are collected both as horological objects and as artefacts of the standardisation of global time; because the type depends on a fixed set of place names, changes in city names, time zones or country borders since manufacture can assist in dating an example, though this requires case-by-case research rather than generalisation.

Sources & references

1. Rawlings, A. L., The Science of Clocks and Watches
2. General manufacturer and patent history for individual world-time clock designs is not verified here.

Where sources disagree, the disagreement is stated rather than resolved silently.