Worldtime watches
References in the Grail Atlas catalog carrying the worldtime complication.
A worldtime watch reads 24 timezones simultaneously through a rotating 24-hour disc paired with a ring of city names representing each zone. Louis Cottier developed the mechanism in the 1930s, and Patek Philippe's collaboration with him produced the 1415 and 2523 — the references that define the category. The traveler turns the city ring to align their current location at 12, and every other timezone reads off correctly without further input.
What to look for
Patek Philippe 5230 and 5330 are the canonical modern worldtimers. Vacheron Constantin's Overseas Worldtime 7700V uses a continent-coloured map disc that is genuinely beautiful in person. Frederique Constant's Manufacture Worldtimer (FC-718) is the value play with an in-house caliber. The two questions are city ring accuracy (the standard ring is missing several actual GMT offsets and treats DST inconsistently — buyer beware if you actually travel) and whether the watch updates the hour hand independently of the local time, which most do not. Most worldtimers are best treated as a beautiful indication, not a navigation tool.