a control panel for regulating plural parameters is provided with plural displays , each associated with one parameter . a single manually moveable knob is provided for entering a manually variable signal . individual actuators such as push buttons are disposed adjacent each of the display means . the control panel is arranged to interpret the variable signal provided by the maneuvering element or knob as a new value for a control constant associated with a particular parameter depending upon which push button is actuated . the operator may select a particular parameter for resetting by pressing the button adjacent the display for that particular parameter . the panel simplifies setting of plural parameters in complex control systems such as the control system for a hemodialysis apparatus . the control system may incorporate plural microprocessors . control data input into the microprocessors is digitally duplicated and transferred between the microprocessors to avoid entry of conflicting data into the two separate microprocessors .