Details requirements for multiturn lead-screw-actuated, and single turn wire-wound, variable resistors with a contact bearing uniformly over the surface of the entire resistive element, wound linearly, when positioned by an actuator, being capable of full-load operation (when maximum resistance is engaged) at a maximum ambient temperature of 85 deg C and suitable for continuous operation, at a maximum temperature of 150 deg C. Their resistance tolerance is 5 percent.