Hourglass, also known as “sand clock”, is an ancient instrument for measuring time. Hourglass manufacturing principle and funnel carving is largely the same, it is based on the amount of sand from a container to another container to measure time. This method of using quicksand instead of water is due to the cold winter air in the north of China, which makes it easy for water to freeze.

The most famous hourglass is the “five rounds hourglass” created by Zhan Xiyuan in 1360. The sand flows from the funnel-shaped sand pool to the sand bucket on the edge of the first wheel, driving the first wheel, thus driving all levels of mechanical gear rotation. The last gear drives the middle wheel rotating on the horizontal surface, and there is a pointer on the axis of the middle wheel, which rotates on an instrument disk with an engraved line to show the moment, and this display method is almost identical with the surface structure of modern clocks. In addition, Zhan Xiyuan also cleverly added a mechanical toggle on the center wheel to remind the two wooden men who stood on the five-wheeled hourglass and beat the drum to tell the time. At every full hour or moment, the two wooden figures would come out on their own and beat the drum to report the moment. This hourglass was detached from the auxiliary astronomical instruments and had become a mechanical clock structure on its own.