An electro-hydraulic circuit enabling two mechanical devices to shadow each other's movements without any direct mechanically-operative linkage between the devices. The two devices incorporate matching sets of hydraulic actuators for inducing movements of movable components of the devices. For each actuator in a given one of the devices, a system of electronic sensors and hydraulic valves, in conjunction with a central processing and control system, keeps track of the physical positions and configurations of the actuator and the corresponding actuator in the other device, and what the status of the actuators should be in relation to each other. If an actuator associated with one device is moved by an external force, a corresponding actuator in the other device moves in response to that external force, with proportionate direction, speed, and force.