In horology, a tourbillon (/tʊərˈbɪljən/; French: [tuʁbijɔ̃]
"whirlwind") is an addition to the mechanics of a watch escapement to increase accuracy. It was developed around 1795 and patented by the French-Swiss watchmaker Abraham-Louis Breguet on June 26, 1801. In a tourbillon the escapement and balance wheel are mounted in a rotating cage, in order to negate the effects of gravity when the timepiece (thus the escapement) is stuck in a certain position. By continuously rotating the entire balance wheel/escapement assembly at a slow rate (typically about one revolution per minute), the tourbillon averages out positional errors.
Originally an attempt to improve accuracy, tourbillons are still included in some modern watches. The mechanism is usually exposed on the watch's face to showcase it.
Today tourbillons represent a great achievement of watchmaking and the complexity of mechanical timekeeping.