Mechanical Principles › Complications › Time zones

WORLD TIME / UNIVERSAL TIME

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1. Definition and purpose of the complication

World time / Universal time is a major horological complication. It simultaneously displays the time in each of the twenty-four time zones. The user can check any time zone without prior calculation or manipulation. This complication appeared as early as the late 19th century, with the adoption of coordinated time zones.

Geneva-based horologist (watchmaker) Louis Cottier developed numerous world time / universal time mechanisms in the 20th century. He thus largely contributed to the advent of this complication in the wristwatch.

The world time / universal time watch differs fundamentally from the dual time zone watch. The latter only displays two times manually selected by the user. The world time / universal time watch embraces the entire globe in a single glance.

2. Display architecture

World time / universal time consists of three concentric display levels on the dial. At the center, the local time is displayed with the hands on a conventional twelve-hour cycle. On the periphery, a ring graduated over twenty-four hours surrounds this central zone. A second concentric ring bears the name of an emblematic city for each time zone.

The city is chosen for its geographical renown and the representativeness of its time zone. Each position on the cities ring corresponds to a one-hour offset from its neighbours. The combination of the two rings allows direct reading of the time for any time zone: the user locates the desired city and reads the time on the twenty-four-hour ring, without any calculation.

3. The two animation modes

Two mechanical architectures make it possible to animate the World time / Universal time rings; they produce the same visual result by inverse means.

Mode 1 — rotating 24-hour ring, fixed cities ring. The twenty-four-hour ring makes one complete clockwise rotation in twenty-four hours, while the cities ring is fixed to the Dial and does not rotate. The 24-hour graduations scroll in front of the fixed city names; the time of the desired time zone is read directly above the corresponding city name.

Mode 2 — fixed 24-hour ring, rotating city ring. The twenty-four hour ring is fixed to the dial. It is the city ring that performs a complete counterclockwise rotation in twenty-four hours. The time zone time is read on the 24-hour ring opposite the desired city. Both modes give equivalent information; the choice belongs to the calibre designer.

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4. Correction using a single pusher

World time correction can be carried out using a single Pusher integrated into the case middle. Each press moves the mobile ring one position, i.e. one hour. This mode only allows incrementing or decrementing depending on the calibre’s construction, which suits travelers crossing few time zones at once.

The correction is carried out without stopping the watch or affecting the movement’s running or the local time setting. A click mechanism holds the ring in place between two successive presses, ensuring the precise alignment of a city with the reading position.

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5. Correction using two pushers

Some calibres feature two pushers distinct: the first increments the value by advancing the mobile ring by one hour, the second decrements it by moving it back one hour. This bidirectional solution is faster for crossing several time zones, avoiding the need to perform twenty-three forward steps to go back a single hour. Each Pusher operates a Click mechanism oriented in the opposite direction, a Neck chain (sautoir) guarantees the precise immobilization of the ring at each hour position.

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6. Correction via the Crown

Correction can also be performed via the Crown, pulled to an intermediate position dedicated to the mobile ring. Depending on the construction of the Calibre, two modes are possible: unidirectional correction, which only allows incrementing or decrementing, and bidirectional correction, which allows both directions depending on the direction of rotation of the Crown.

This solution avoids adding Pushers and correctors to the Case middle, and is suitable for elegant watches where their presence would be aesthetically undesirable. Moreover, it allows completely avoiding any unintentional correction due to a shock or unwanted pressure on a Pusher.

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7. Seasonal time change

The World time / Universal time watch is sensitive to seasonal time changes. The cities listed on the ring are positioned at fixed offsets relative to UTC. No correction can be made city by city: the ring is a single, integral assembly. The difference between Time zones is therefore constant and does not account for the different zones applying seasonal time changes.

Today, a few rare watches incorporate a complex mechanism capable of distinguishing winter time from summer time, but they remain limited in their display possibilities.

8. Combination with other complications

Combining world time / universal time with other complications is complex, due to the concentricity of displays required by world time / universal time and the legibility (cities and 24-hour ring) required. Thus, world time / universal time will more readily be paired with a minute repeater or a tourbillon than with a perpetual calendar or a chronograph.

9. History and origins

The World time / Universal time complication emerged as early as the late 19th century, accompanying the international adoption of coordinated time zones at the 1884 Washington Conference, which defined the Greenwich meridian as the world reference. This standardization created the need to indicate several times simultaneously on a single dial.

Geneva-based Horologist (watchmaker) Louis Cottier developed numerous World time / Universal time mechanisms, contributing greatly to its adoption by Swiss manufacturers. The complication remained reserved for haute horlogerie for a long time due to its complexity and production cost.

Its spread widened from the 1980s onward thanks to new manufacturer calibres. Contemporary production offers this complication across various price segments. It remains a recognized marker of travel-oriented haute horlogerie, along with the dual time zone watch.