A mechanism that rotates the balance and escapement in a cage to average out gravity-related timing errors in vertical positions.
In a tourbillon, the escapement and the balance are mounted in a rotating cage of 50 to 80 small parts. The escape wheel meshes with a fixed wheel on the main plate, and the turning cage carries the regulating organ through every vertical position. Most cages turn once a minute, which lets a hand on the cage show the seconds. A faster cage mixes positions more often but uses more of the power reserve.
Its purpose is narrow. Because a balance and its spring always have slight asymmetries in mass, gravity disturbs the rate in each vertical position; rotating them averages those errors out. With the watch lying flat there is nothing to average, so the benefit was clearest in pocket watches, which spend most of their time upright. In a wristwatch, the advantage is debatable. A tourbillon compensates for position; it does not make every watch more accurate. It is still counted as a complication.
In job listings
Tourbillon is rarely named in job listings. The work falls to watchmakers who assemble and service complicated movements, and to movement designers who develop them; listings for these roles often speak of complications rather than of a single mechanism. See current watchmaker roles.
