Detent escapement The detent escapement is a detached type of escapement. It allows the balance wheel to move freely, swinging undisturbed through most of its cycle (except the brief impulse period, which is given only once per cycle or every other swing), thus maximising its isochronism. Because the driving escape wheel tooth moves almost parallel to the pallet, the escapement has minimal friction and does not need oiling. For these reasons, among others, the detent was considered the most accurate escapement for balance-wheel timepieces. The detent escapement was invented by French Watchmaker Pierre Le Roy in 1748. Le Roy's design was considered ineffective, and it was not until 1775 that John Arnold improved upon the design and was the first to use the detent escapement with an overcoil balance spring (which he patented in 1782). With this improvement Arnold's watches were the first really accurate pocket timekeepers, keeping time to within one or two seconds per day.
