Typical of them is Jagyokru manufactured in 1434, which is an automatic clepsydra made on the basis of water stream and buoyancy of materials in vessels. Devices ringing bell, tambourine and gong were combined with each other to tell the time at an interval of two hours.

Angbuilgu, made in the same year, is a sundial. It consists of a semi-coplanar vessel and a stick which makes a shadow on the vessel. The 24 divisions of the year in the lunar calendar were marked on the surface of the vessel. Angbuilgu was higher in accuracy than a sundial with flat shadow plate.

There is also Okrugiryun installed on a building of Kyongbok Palace in 1438. This time measurement apparatus has the same devices with Jagyokru. As it correctly showed the ever-changing positions of sunrise and its movement according to seasons, the apparatus played the role of an astronomical instrument at the same time.

The noontime measured by those apparatuses almost coincided with the present one based on 127 degrees 30 minutes of east longitude.