The principle of mechanical clocks at early stages
The earliest mechanical clock in the world is called "tower clock", which was successfully invented around the 13th century. Unlike a watch, this kind of clock is mounted on a high tower and uses the force of a heavy hammer to drive the gear, which then drives the pointer to move, and uses an "escaper" to control the speed of the gear to get a more accurate time. However, a clock driven by a heavy hammer can only be erected high on the tower, which is very inapplicable.
