Torque is the twisting force exerted at a point of rotation by a force applied at the end of a lever arm (torque = force x lever arm). A reciprocating engine converts the up-and-down motion of the pistons into the rotary motion of the crankshaft using a conrod, producing an effective torque at the crankshaft's end. The transmission turns this torque into tractive force. The physical unit for measuring torque is the Newton-metre (Nm). Today's engines should be designed to deliver as much torque as possible both from low rev speeds and over a wide rev range. This makes for good in-gear acceleration and means that drivers do not have to change gear as often, thereby saving fuel. An engine's performance characteristics can be deduced from its output (kW) and torque (Nm). Virtually all engines built by Volkswagen are designed for favourable torque characteristics, i.e. they permit a style of driving with a low gearshift frequency.