The Sundial (Ri Gui) in Beijing Forbidden City

Round in shape, this sundial is made of white marble stone, with graduations on both sides. The gnomons are made of iron, and placed vertical to the dial. The square base of the dial is supported by four stone pillars. The dial is located on a base obliquely, parallel with the equator. The gnomons point to the North and South Poles, respectively. The sundial is a device which during hours of sunlight indicates the time by a shadow cast by a gnomon on a dial marked in hours. During the six months from the Spring Equinox to the Autumn Equinox, the graduations on the surface of the dial (or to the north of the equator) indicate the time: and during the six months from the Autumn Equinox to the Spring Equinox, the graduations on the back of the dial (or to the south of the equator) tell the time.

The placing of the sundial in front of the hall symbolizes that the emperor had the highest power to grant time to all the people in the country.