One of the important instruments for determining positions of celestial bodies in ancient China. This instrument was made in 1437 (Ming Dynasty). It consists of three ring systems, from which the equatorial, ecliptic and horizontal coordinates of celestial bodies could be measured. On those rings both scales of 365.25 and 100 divisions were graduated. These kinds of scale systems possess distinguishing features of ancient astronomy of China. It was pillaged by German troops when the Eight-Power Allied Forces invaded Beijing in 1900. It was returned to China in 1920.