This portable astronomical instrument known as an astrolabe was used to locate the positions of the stars and to determine local time, latitude and longitude. It was made and used in many parts of the world in the past and in the medieval Islamic world in particular. This particular one was made by Ryu Geum (1741-1788), an expert in geometry and astronomy who also maintained friendly relations with Bukhak scholars including Bak Ji-won (1737-1805). There is a seal on the top of the front face bearing an inscription composed of three Chinese characters, "柳氏琴", along with a memo that it was "made in 1787 for Master Yun, or Yagam" [his courtesy name].