Lever escapement "draw" its action is very precise. Third, it is self-starting, so if the watch is jarred in use so the balance wheel stops, it will start again. A cheaper and less accurate version of the lever escapement, called the pin pallet escapement, invented by Georges Frederic Roskopf in 1867, is used in clocks and timers. The escape wheel is geared to the watch's wheel train, which applies torque to it from the mainspring. The rotation of the escape wheel is controlled by the pallets. The escape wheel has specially shaped teeth of either ratchet or club form, which interact with
Escapement was unworkable. Arnold also designed a spring detent escapement but, with improved design, Earnshaw's version eventually prevailed as the basic idea underwent several minor modifications during the last decade of the 18th century. The final form appeared around 1800, and this design was used until mechanical chronometers became obsolete in the 1970s. The detent is a detached escapement; it allows the balance wheel to swing undisturbed during most of its cycle, except the brief impulse period, which is only given once per cycle (every other swing). Because the driving escape wheel tooth moves almost parallel to the pallet, the escapement