Sundials were used by ancient people to calculate what

Ancient Chinese time measuring instrument. The use of the shadow cast by the sun to determine the moment of the device

Sundial, also known as the "sun gauge", is China's ancient use of the shadow of the sun to measure the moment of a time instrument. The principle is to use the shadow cast by the sun to determine and divide the moment. Sundial is usually made of copper pointer and stone disk composition. This use of the sun's projection to timekeeping method is a major invention in the field of astronomical timekeeping, this invention has been used by mankind for thousands of years. By the sundial needle and sundial plate, sundial plate has a time scale, sundial needle perpendicular to the plate, through the sundial needle shadow in the direction of the plate can be measured time. Placed on the plate because of the direction of the different sundials can be divided into horizon sundials, equatorial sundials, sundials, sundials, oblique sundials. The early history of the sundial is not clear, the earliest reliable records are "Sui book - astronomy" mentioned in the Yuan Feng in Sui Kaihuang fourteen years (594) invented the short shadow leveling instrument (i.e., the ground level sundial). The equatorial sundial is clearly documented in the Southern Song Dynasty Zeng Minxing "sole awake magazine" volume 2 mentioned in the sundial shadow map, but the sundial plate is made of wood. Later generations switched to stone sundial plate, metal sundial pin. The Forbidden City in Beijing and other places to preserve the stone equatorial sundial made in the Qing Dynasty. Equatorial sundial sundial parallel to the equatorial plane, the sundial needle points to the north and south poles.