The tourbillon was invented by Abraham-Louis Breguet around 1800. The aim was to correct vertical position errors. The balance together with balance spring and escapement is mounted in a rotatable frame, known as the cage, and is driven by the seconds wheel sitting underneath the balance. The tourbillon (French: whirlwind) is one of the most challenging grand complications. A variation of this is the flying tourbillon, invented by Alfred Helwig in 1920. It is cantilevered, being only supported on one side.