The front wall of the elongated case of a linear motion potentiometer is provided with a longitudinal slot, in which a slide is disposed. The slide carries a bridging contact inside the case, where it engages spaced parallel resistor and collector elements. In front of the case and parallel to the slot are a stationary lead screw and a manually rotatable cylindrical drum, both supported from the case. The drum, when rotated, rotates internally threaded cylindrical means mounted on the screw and thereby moves it along the screw and drum. The slide is connected with the rotatable means so that the slide will be moved lengthwise of the case when the drum is rotated.