The sensor is adapted for sensing relative displacement of a relatively movable body. The sensor (1) comprises an elongate member (16) longitudinally slidable in a housing (33) in dependence on the relative displacement of a body (10). The elongate member has a longitudinal engagement surface provided for example with teeth (18) which engage with teeth provided on the periphery a rotatable member (19) mounted for rotation in the housing. The rotatable member is associated with an arm (21) which may carry an indicator (23) at its end which is movable with rotation of the rotatable member over a scale (22). The assembly comprising the elongate member, the rotatable member and the arm is arranged to be substantially balanced about the axis of the rotatable member with a slight resultant force on the elongate member tending to move it in the direction of the body. For this purpose, the assembly may include a spring (25) acting for example on the rotatable member. |