Guess it was a code for store/floor display mode. The husband had pushed too hard on the electronic interface front so it hung by one screw. Gentle use allowed function for 3 years. Then we shut off the electricity because could not shut off the oven light. Plug back in, no oven pre-heat, no oven. Sent for the part, and used the internet; a very knowledgeable lady on your end when I couldn’t see what part #20-a meant. She explained about a sticky faceplate. Plugged in wires when the part came the next day, voila, I can cook the turkey!