The Equatorial Armilla was made in the eighth to twelfth year of the reign of Emperor Kangxi (1669-1673), under the supervision of the Belgian missionary Ferdinand Verbiest. Its design referenced the astronomical instruments of the famous European astronomer Tycho in the 16th century. This instrument weighs 2720 kilograms and is 3.380 meters high, located on the top platform of Beijing Ancient Observatory. It is mainly used to measure the equatorial longitude and latitude of celestial bodies and true solar time.