Generally patients determine their own personal best value. This is the highest value the patient can achieve under optimum conditions (free of symptoms, feeling well). [Example: 500 l/min.] The green area usually reaches 80% of the personal best value. [Example: 500 l/min x 0.8=400 l/min] The yellow area usually reaches 50% of the personal best value. [Example: 500 l/min x 0.5=250 l/min].