The speedometer indicates the speed of the vehicle. It shows the instantaneous speed, which is why the pointer shakes. You will understand the principle of the speedometer below.

The indication of the speedometer depends on the speed sensor. The sensor is installed on the gearbox. Different pulse signals are obtained through different speeds, and then converted to pointer output, which is the current speed you see. The regulations require the speedometer to display slightly higher than the actual speed, which is for safety. Another is the liquid crystal display speed. The principle is similar to the above, and the indication output is replaced by liquid crystal display.

Source: @adamdarklordjones