The “traffic light scheme” allows a patient to self-assess measured values to follow the progression of the illness. Self-assessment empowers patients to control their asthmatic illness in close co-operation with their physician. The physician determines a green, a yellow and a red area for the patients peak flow readings. As long as the values are in the green area, the lung disease is well under control. If the readings are frequently in the yellow area, the medication dosage should be increased according to the physician’s recommendation. Peak flow results in the red area are dangerous! The patient should act as recommended by the physician or seek emergency medical treatment.