A sundial is also called a gnomon. It was used in ancient days for measuring the position of the shadow of the Sun in order to determine the time in a day. The most primitive sundial was to erect an eight-foot bamboo pole on the ground. During Zhou Dynasty, the sundial had been ameliorated and was called Gui-Biao. Gui is a ruler made of jade and placed on the ground. Biao is an eight-foot wooden pole erected on the ground. In the Han Dynasty, a copper pole was used instead. Based on their structures, sundials can generally be divided into three main designs: equatorial, horizontal, and vertical.

The dial of an equatorial sundial is in parallel to the equator. The pole itself passes through the center of the dial vertically and is parallel to the axis of the Earth, pointing to the North Pole.

A horizontal sundial uses a triangular sloping piece erecting on the horizontal surface to be the pole. The pole points to the north-south direction. The dial can be in the shape of a semicircle. The inclination angle of the pole slope is the same as local latitude. This kind of sundial is easy to make. It is suitable for mid-latitude regions and quite common.

A vertical sundial is installed on the wall of a building. The wall is vertical to the ground, while the sundial is placed flat or drawn on the surface of the wall. As the wall can face in different directions, there are different vertical sundials facing south, north, east, west, or other directions; the poles are installed accordingly.