Watches were first invented for navigation at sea. The watch and the sun are used to determine the position. The principle is also very simple, although the linear speed of the sun's movement is different, but the angular speed is fixed, 15 degrees per hour. And the hour hand of the watch is 30 degrees per hour. This is exactly two times the angular speed of the sun, and the sun is located in the south at noon, when the hour hand and 12 o'clock coincide. This method can also be used to calibrate the time, that is, with the compass, when the sun runs to the south, adjust the time to the 12 o'clock position.
How to confirm the south? The watch face is placed horizontally and the hour hand is aligned with the direction of the sun, then the direction of the angle bisector between the hour hand and the 12 o'clock position of the dial is the south.