The tourbillon escapement compensates the effects of gravity: the balance and escapement are mounted in a small moveable cage which revolves once a minute and, by doing so, compensates for rate errors. The invention was patented by Abraham-Louis Breguet on 26 June 1801 (7 Messidor Year IX of the Republican Calendar). Inextricably linked to his name as its inventor, the tourbillon regulator is a system designed to compensate for errors and fluctuations in the workings of watches due to unavoidable changes of position. The invention comprises mounting the escapement on a moveable platform (or cage) which completes one revolution in a given period of time, often one, four or six minutes. The regularly repeating errors offset one another. The Tourbillon is one of the most well-known inventions of Abraham-Louis Breguet and is also one of the most difficult to produce. Archives show that 35 examples were sold between 1805 and 1823.