Escapement remontoire, a device which isolated the escapement from changes in drive force. Without a balance spring, the crossbeat would have been no more isochronous than the verge. Invented around 1657 by Robert Hooke, the anchor (see animation at top of page) quickly superseded the verge to become the standard escapement used in pendulum clocks through the 19th century. Its advantage was that it reduced the wide pendulum swing angles of the verge to 3–6°, making the pendulum nearly isochronous, and allowing the use of longer, slower-moving pendulums, which used less energy. The anchor is responsible for the long narrow shape
Escapement to a point close to its unstable state, and is released with a snap each swing of the balance wheel to give the wheel an impulse, after which it is cocked again by the wheeltrain. The advantage claimed is that since the blade imparts the same amount of energy to the wheel each release, the balance wheel is isolated from variations in impulse force due to the wheeltrain and mainspring which cause inaccuracies in conventional escapements. Parmigiani Fleurier with its Genequand escapement and Ulysse Nardin with its Ulysse Anchor escapement have taken advantage of the properties of silicon flat springs.