A power servo system which includes an actuator (12) coupled to a load and receives an input command signal (R) indicative of desired motion at the load. A sample-data control system (20) receives and samples input signals (R, Y) indicative of desired and actual motion at the hydraulic actuator and load, and provides drive signals (U(Z)) to the actuator necessary to obtain desired motion. The sampled-data control system (20) includes digital processing circuitry (22) with series and feedback compensation (32, 281, coordinated with the hydraulic system transfer function,to form a complete closed-loop control system operating in the sampled-data or Z-transform domain. Different equation constants (C,, C 2 ,C 3 and G 1 , G 2 , G 3 ) in the series and feedback compensation circuitry are recalculated periodically. In one embodiment of the invention (Figure 3), such constants are recalculated as a function of system behavior, so that system control automatically varies with operating conditions. In other embodiments of the invention (Figures 4 and 5), system constants are calculated based upon a single operator-variable (or remote system) input (a), which accommodates rapid operator-implemented tracking of system behavior while reducing calculation time.