In clinical practice, patients with acute myocardial infarction are often required to have an ECG every half hour or some time, and the anterior chest wall of the patient is marked with gentian violet or other dyes so that the electrodes are placed in a relatively fixed position every time the ECG is done. This is because in acute myocardial infarction, the physician has to continuously observe the changes in the ECG to determine the height and width of the QRS waves, the changes in the ST and T waves, and to determine the derivation process of acute myocardial infarction. placement should be relatively fixed.