Abstract: A potentiometric circuit arrangement 30 is based on a resistive potentiometer tarck 11 with a capacitively coupled `wiper` 14', the resistive track being driven by switched alternating voltages of +/- V at 12 and -/+(X-V) at 13, where X is a reference voltage and V is the output of an integrator 15 to which the voltage sensed by the elecrode 37, and rectified at 36, is applied. A null voltage point establishes itself at the position of the electrode and stabilizes the integrator output at a d.c. voltage proportional to the distance of the `wiper` from the track end 12. Any `wiper` displacement taps a non-null signal which integrated applies new voltages to the track until the null point is re-established at the `wiper` position. The capacitive pick-up enables a potentiometer-type voltage output with less wear of the track, less drag against motion and less electrical noise, and electronic differentiation (27) of the position signal to give a rate signal.