A control system for a combine harvester having a crop processing system with a control panel for enabling an operator of the combine harvester to set a plurality of operating parameters of the crop processing system that affect the harvesting performance, and a plurality of sensors for determining prevailing values of crop quality parameters. The control system includes a data processor having a display for communicating information visually to the operator and acts to determine when a crop quality parameter exceeds an unacceptability threshold. Following such determination, the control system displays to the operator an operating parameter of which adjustment is recommended in order to restore the crop quality parameter to an acceptable value. The recommended operating parameter is derived from data stored in a look-up table within the data processor.