Abstract: A variable resistor with a dual ratio input shaft that permits rapid and precise adjustment of the voltage or current level in an electric circuit. A single shaft operates the respective drive elements in the mechanism to provide variable control from a single control knob. The shaft is longitudinally slidable between two drive positions. One drive position allows more rapid adjustment of the resistance value for each turn of the control knob than the other drive position which permits more precise adjustment of the resistance value for each comparable turn of the control knob.