Final answer:
The FEV1/FVC ratio measures lung function and can diagnose lung diseases such as asthma or fibrosis.
Step-by-step explanation:
The ratio FEV1/FVC measures lung function and is used to diagnose lung diseases such as asthma, emphysema, and fibrosis. A high FEV1/FVC ratio indicates stiff lungs and lung fibrosis, while a low ratio suggests resistance in the lungs, characteristic of asthma.