The Avro RJ control panel is based on the 737 (Honeywell) design; if the alt selector knob is spun fast towards the new value or the knob stops between detents, the system detects an invalid input and flashes the display. With a flashing display the knob should be turned to select / reselect the correct alt sel value as the alt capture may not work. A similar flashing display and / or large value displayed (50,000ft ?) indicates other failures.