The models Optima Timer, Look® Selection, Look® DeLuxe, Look® Timer, Aroma Signature, Aroma Signature DeLuxe, AromaElegance® and AromaElegance® DeLuxe have a descaling indicator as part of their 3-in-1 limescale protection system. A continuous red light in the CALC button (Look® series of appliances, Optima Timer) or the DECALC button (Aroma Signature series of appliances, AromaElegance® series of appliances) indicates that the appliance should be descaled. The CALC / DECALC button illuminates based on the water hardness you have set, when this button lights up you should descale promptly. The light will go out after the descaling programme has been completely carried out. Detailed information on descaling and caring for your filter coffee machine can be found in the enclosed operating instructions.