1, the maximum time of the hourglass is not known, but the average hourglass has a nominal working time of 1 minute.

2, The hourglass, also called a sand clock, is a device for measuring time. The Western hourglass consists of two glass spheres and a narrow connecting tube. Time is measured by the amount of time it takes for the glass balls filled with sand to flow from the top through the narrow pipe into the bottom glass ball. Once all the sand has flowed into the bottom glass ball, the hourglass can be inverted to measure time.

The most famous hourglass is the “five-wheeled hourglass” created by Zhan Xiyuan in 1360. Sand flowed from a funnel-shaped sand pool into a bucket on the side of the first wheel, which drove the first wheel, which then drove mechanical gears at all levels to rotate. The last gear drives in the horizontal surface of the rotation of the wheel, the wheel of the center of the axis of a pointer, the pointer is in an instrument with a line on the disk rotation, so as to flash the moment, this flash method is almost identical with the surface structure of modern clocks. In addition, Zhan Xiyuan also wonderfully added a mechanical toggle device on the center wheel to remind the two wooden men who stood on the hourglass of the fifth wheel to cut the drum to tell the time. At every full hour or moment, the two wooden men would come out on their own and cut the drum to report the time. This hourglass is detached from the auxiliary astronomical instruments, and has become a mechanical clock structure independently.

Because there is no water pressure line system, the hourglass is more accurate than the leaky carving.