Abstract: A servosystem is comprised of an energy-storing controlled system having an output variable which is to be maintained at a predetermined value. An energy-varying unit, for example a source of electrical energy, is connected to the controlled system for energizing the latter. Alternatively, the energy-varying unit could be operative for removing energy from the controlled system. A two-mode control unit is operative in the first mode thereof for causing the energy-varying unit to effect a change in the energy stored by the controlled system, and is operative in the second mode thereof for preventing the energy-varying unit from effecting such change. An error-indicating unit is operative for generating an error signal indicative of the deviation of the output variable of the controlled system from the predetermined value to be maintained.