Abstract: An electrical device is disclosed which is small in size and easily assembled. The device employs a rotatable housing and a grooved geometrically programmed disc to locate a ball contact at a desired position on a substrate. The substrate may comprise a resistor, spaced contacts or other conductive surface, and the movable ball contact may change circuit conditions incrementally when compared with the degree of movement of the drive for the ball. The ball has two points of contact with the grooved disc reducing noise and wear. The grooved disc is readily replaceable for changing the operating characteristics of the device.