Continuous positioning system

The system has a ring gear connected to a backrest and an assembly (37) with moving and blocking parts. The moving part contacts a ramp to rotate gear with assembly, in an active position and is away from the ramp to rotate freely the gear and assembly, in an inactive position. A device (10) rotates in reverse direction with respect to a positioning part and the blocking part. An independent claim is also included for a seat of a motor vehicle.