This escapement, which has finally ousted all others in mechanical balance-controlled timekeepers, was first invented in the mid 18th century, although its merits were not fully appreciated until the second quarter of the 19th century, when it began to be produced in large quantities. The lever escapement may be classified in three main types, the action being identical in each case. The first type, made mostly by the English, has all the lift or impulse on the pallets, and the escape wheel has ratchet-type teeth. The second type has what is known as 'divided lift', i.e. Some of the time pulse is on the escape-wheel teeth, which are of club shape, and the remainder of the lift is on the pallet stones. This form is fitted to most good-quality balance-control clocks today. The third type is the pin pallet, which has all the lift in the escape-wheel teeth. It is found in low-quality clocks and, although cheap to make, suffers from disadvantage of rapid wear, mainly because of poor oil retention. The disposition of the parts allows further classification: English makers usually mounted the lever arm tangentially to the escape wheel, the balance, pivot and escape-wheel pivot holes making a right angle, while the Swiss planted the pivot holes of the balance, pallets and escape wheel along a straight line. The escape wheel to pallets action is similar to the dead-beat escapement with one major exception, which is that the pallet stones are angled on their locking faces to give a small amount of recoil, used to draw the lever on to the banking pins. The forked end of the lever is about to receive the impulse pin. The balance is rotating anticlockwise, the impulse pin entering the lever fork, moving the lever to the left, and unlocking the escape wheel and receiving impulse. The escapement then re-locks on to the opposite pallet, and the balance continues its anticlockwise swing. The draw on the pallet stone moves the lever to contact the banking pin, making contact between the guard pin and the guard roller unlikely. Frictional-rest escapements, such as the cylinder or duplex, suffer from the interference caused during the locking. In the lever escapement, interference is isolated from the balance during most of its swing, thus detaching the balance from its driving force, except during unlocking and impulse, and gaining the name 'detached-lever escapement'.