Peak flow meter: This device helps people with asthma see how well their lungs are working. Changes in normal values give an early warning of an asthma attack. As a general rule, children over the age of six or those in first grade are physically able to use a peak flow meter in conjunction with their Asthma Action Plan. A primary care physician may choose to prescribe a peak flow meter for children under the age of six. (PG 2002.01)