A peak flow meter is a portable, inexpensive, hand-held device used to measure how air flows from your lungs in one "fast blast." In other words, the meter measures your ability to push air out of your lungs.
Peak flow meters com in two ranges to measure the air pushed out of your lungs. A low-range peak flow meter is for small children, and a standard-range peak flow meter is for older children, teenagers and adults. An adult has much larger airways than a child and needs the larger range.