The main manifestations of asthma are coughing, wheezing, chest tightness and breathlessness. The most common manifestation is coughing, so many people use the presence or absence of coughing to determine whether an asthma attack is occurring, and use the severity of coughing to determine the severity of an asthma attack. In fact, this is inaccurate. Some people do not cough at all when they have an asthma attack, some show chest tightness and breathlessness, but children often cannot say what these feelings are; sometimes children cough just from a cold or bronchitis, not from an asthma attack. Having the peak velocity measured gives us an objective and valuable indicator of the presence or absence of an asthma attack, the extent of the attack, and the efficacy of the asthma control medication. This is like taking blood pressure in patients with hypertension, and the medication should be adjusted according to the result of blood pressure measurement, not according to whether there is headache or dizziness or discomfort. There are many parents of children with asthma who reduce or stop their own medication based only on the fact that their children do not cough for a period of time, resulting in uncontrollable asthma, good and bad, and repeatedly.