Tourbillon

Definition

A rotating cage that holds the balance wheel and escapement, designed to counteract the effects of gravity on timekeeping accuracy. It was patented by Breguet in 1801 for pocket watches, which sit in one position; its practical value in a wristwatch, which does not, is debated. It stays uncommon: 531 of the 17,435 watches in this catalogue carry one in the model name — see what rarity means here.