A tourbillon (IPA: [toɹ bi ˈjɑn], French for "whirlwind") is a type of mechanical clock or watch escapemen invented in 1795 by Abraham-Louis Breguet that is designed to counter the effects of gravity and other perturbing forces that can affect the accuracy of a chronometer. This is accomplished by mounting the escapement in a rotating frame, so that the effect of gravity cancels out when the escapement is rotated 180°. The effects of gravity were particularly problematic when pocketwatches were carried in the same pocketed position for most of the day. In a tourbillon, the entire escapement assembly rotates, including balance wheel, escapement wheel, and pallet fork. The rate of rotation varies per design but has generally become standardized at one rotation per minute.

The tourbillon is considered to be one of the most challenging of watch mechanisms to make (although technically not a complication itself) and is valued for its engineering and design principles. In modern watch designs a tourbillon is not required to produce a highly accurate timepiece. Nevertheless, the tourbillon is one of the most valued complications of collector's watches and premium timepieces. In fact, modern implementations typically allow the tourbillon to be seen through a window in the watch face. In addition to enhancing the charm of the piece, the tourbillon acts as a second hand as it rotates once per minute.

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