Hourglass also known as " "Sand clock" is an instrument for measuring time in ancient my country. Hourglasses are made in much the same way as stencils, which measure time based on the amount of quicksand leaking from one container to another. This method of using quicksand instead of water is because the air in northern my country is cold in winter and the water is easy to freeze.

The most famous hourglass is the "five-wheeled hourglass" created by Zhan Xiyuan in 1360. The quicksand flows from the funnel-shaped sand pool to the sand bucket beside the primary wheel, driving the primary wheel, thereby driving the mechanical gears at all levels to rotate. The last stage gear drives the middle wheel that rotates on the horizontal plane. There is a pointer on the axis of the middle wheel, and the pointer rotates on a scaled instrument disc to display the time. This display method is almost the same as that of modern clocks. The surface structure is exactly the same. In addition, Zhan Xiyuan also cleverly added a mechanical toggle device to the middle wheel to remind the two wooden figures standing on the five-wheeled hourglass and drumming the time. Every hour or quarter, the two wooden figures would come out on their own and beat drums to report the time. This hourglass is separated from the auxiliary astronomical instruments and has become a mechanical clock structure independently.