When measuring lung capacity, the correct blowing method is: first take a deep breath, inhale deeply and lift up the chest, then aim the mouthpiece at the mouth, use both hands to force the handle against the mouth, and press the mouth forcefully downward against the skin around the mouth, subject to no air leakage. Then exhale slowly and evenly. Attention should be paid to the even speed, not too fast or too slow. Too fast will result in a short blow until all the breath is exhaled from the lungs. Also straighten your body during inhalation and try to take in enough air; try to keep your body leaning forward all the way during exhalation. This is the correct method of blowing lung capacity. Its determination depends mainly on the degree of relaxation of the chest wall in expansion and contraction. The lung capacity of adult men is 3500ml~4000ml, and that of women is 2500ml~3000ml. Because spirometry is easy and reproducible, it is a commonly used indicator for health checkups.