Among them are a sundial called Angbuilgu and clepsydras Jagyokru and Okrugiryun made in the period of the Feudal Joson Dynasty (1392-1910).

The noontime measured by them exactly coincided with the present one based upon 127 degrees 30 minutes of east longitude.

Jagyokru was made by engineers including Jang Yong Sil in 1434 and installed in Kyongbok Palace. In the same year, Korean astronomers and engineers manufactured Angbuilgu.

Okrugiryun, made in 1438, had played a role of an astronomical instrument.