Abstract: Apparatus for sensing the extent of rotation of a rotatable part relative to a fixed part, comprises a pair of rings one of which is fixed and the other is rotatable, which define between them an annular space. Disposed in the annular space is a third ring carried by the rotatable ring, whose rotated position is sensed by a device carried by the fixed ring, by any of a variety of mechanisms, in a manner and to an extent such as indicates the degree of rotation of the rotatable part. At least one switch actuator is carried by the third ring and a switch device is carried by the fixed ring. The switch actuator also detects the extent of relative movement between the third ring and the fixed ring.