A computer controlled hydraulic resistance device for apparatus such as a prosthetic knee for above knee amputees, includes a two stage pilot operated solenoid valve connected to control the flow of hydraulic fluid to and from a hydraulic actuator which applies resistance to the prosthetic knee or other apparatus through a coupling. Hydraulic pressure is sensed on the high and low side of the actuator by a spring biased magnet and a magnetically actuated electronic sensor and is used by a micro-controller in a closed-loop manner to compensate automatically for variations in the device and in the hydraulic fluid viscosity. The device also has magnetically actuated electronic sensors which sense positions of the apparatus and feed back to the micro-controller for applying a predetermined resistance profile to the apparatus.