Square Table - 正方寨

The Square Table (Zhèngfāng Zhài - 正方寨) was designed by Guō Shǒujìng 郭守敬 during the Yuan Dynasty (1279-1368). It was used to measure the azimuth of celestial bodies by the equal altitude method and could also be used as protractor.

Detail of Guo Shoujing's Square Table - 郭守敬的正方寨的特写