Capacitance pen's principle is to simulate human fingers through conductors. When the pen tip touches the capacitive screen, it will also generate current, and the controller will calculate the current to get the touch information and complete the operation. Capacitive touch screen is composed of four layers of composite glass, and the inner surface and interlayer of each glass layer have a layer of ITO conductive material, which makes the induced voltage form the capacitance of the current change area, so that the IC at the four corners can judge the coordinate position of the induced area. Capacitive touch screen works by current induction of human body. When a finger touches the metal layer, a coupling capacitance is formed between the human electric field, the user and the touch screen surface. For high frequency current, the capacitor is a direct conductor, so the finger draws a small current from the contact point. This current flows from the electrodes at the four corners of the touch screen, and the current flowing through these four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position information of the touch point through the accurate calculation of these four current ratios.