smart board price comparison.Although the body is far away from the capacitive touch screen, it is much larger than the finger area. They directly measure the touch position. In addition, in theory, many linear relationships should be nonlinear. For example, the total amount of current drawn by people with different body weights or different finger wetness is different, and the change of total current and the change of four partial currents. It is a non-linear relationship. The custom polar coordinate system of the four corners used in the capacitive touch screen does not have an origin on the coordinates. After the drift, the controller cannot detect and recover. Moreover, after the four A/Ds are completed, four points are obtained. The calculation process of the value of the flow rate to the x, Y coordinate value of the touch point in the Cartesian coordinate system is complicated. Since there is no origin, the drift of the capacitive screen is cumulative, at work