Ratchets are devices that constrain rotational or linear motion to one direction exclusively. This design may be used to develop a mechanism that allows the limited motion's direction to be adjusted. The word "ratchet" comes from the French word 'raquette', which means "little wheel". Technically, all reciprocating mechanisms use a ratchet device to prevent rotation in the opposite direction. There are two types of ratchet mechanisms: pawls and cams. In both cases, the ratchet mechanism includes some sort of locking element that can only take one position at a time. This locking element may be a pawl that fits into a groove on a gear, or it may be a rocker arm that can only point one way. When the pawl or rocker arm is in its locked position, it prevents the gear from turning in the other direction. The pawl type ratchet mechanism was invented by Francois Verguin in 1769. It consists of a piece with notches on it called a pawl that fits into a corresponding set of grooves on a gear. As the pawl turns, each notch will align with a corresponding groove not to allow the gear to rotate. The cam type ratchet mechanism was invented by Samuel Winters in 1872.