A sudden, steep drop may signal an oncoming attack. But not every person with asthma needs a peak-flow meter. If your disease is already well-controlled and you rarely have attacks, you may not need to regularly monitor your breathing. Ask your doctor if a meter is right for you. This is up to you and and your doctor.
Many people take two measurements each day, one in the morning and one in the evening.
Whatever your schedule, you should measure yourself at close to the same time each day. You should also use your meter during situations that are especially hard on your lungs. For instance, if you sometimes have an attack while exercising, check your breathing before and after you work up a sweat. If your airways are already tight, you may have to skip the workout. You can also check your breath in the middle of the workout to see if an attack is on the way.