The touch points on the fully transparent touch screen correspond to a “function switch”. When the finger touches this switch area, the corresponding "function program" will start immediately and execute a preset series of commands. The key technology of the touch screen is to measure the exact position (ie coordinates) of the touch point. For example, the “surface acoustic wave touch screen” is equipped with horizontal and vertical ultrasonic transmitters in the upper left and lower right corners, and the upper right corner is equipped with Two corresponding ultrasonic receivers. The ultrasonic transmitter always emits ultrasonic waves during operation of the touch screen. When people touch the screen, their fingers block and absorb some of the ultrasound, which attenuates their energy. At this time, the ultrasonic receiver can calculate the coordinate value of the finger based on this, thereby obtaining the exact position of the finger and reacting.