Why should a Peak Flow Meter be used as part of a regular treatment plan? - A Peak Flow Meter measures the force of the air expelled from your lungs. It will help give you an early warning if your airways start to deteriorate. Your treatment plan can include what steps to take when your Peak Flow Meter is in the green, the yellow or the red zone. This could save you a trip to the emergency room. Discuss the use of a Peak Flow Meter with your physician or respiratory therapist.