The invention provides integration of the automatic semiautomatic and manual modes on a single man-machine interface device (200,400), with the master control of a system parameter such as pressurizer level, which is responsive to at least two system components (charging pumps, letdown valves), each of which can adjust a different system variable. The setpoint for automatic master control, is selected and displayed (216) on the device, along with the current value (212) of the setpoint parameter (pressurizer level). In the semiautomatic master mode selectable by the operator on the device, either a setpoint (272) or an output demand (282) can be specified for one of the components (206), and the master controller will then adjust the other component (204) accordingly. When all subgroup controls are in the manual mode, the master controller is completely overridden by operator control of each component or subgroup.