Angbuilgu is the name given to a pair of sundials that were made by three scientists of the Joseon Dynasty, Jang Yeong-sil, Yi Cheon and Kim Jo, in 1434, the 16th year of the reign of King Sejong the Great. The name means “pot-shaped sun clock staring at the sky”, and the hemispherical shape represents the shape of the Earth. This kind of sundial is very useful for telling the time and the season even though the size may be small. The larger one has a 35.2 cm diameter and 14 cm height, and was produced in the latter half of the 17th century, while the smaller one has a 24.3 cm diameter, and was produced in the first half of the 18th century. There are 7 vertical and 13 horizontal lines on the concave plate of the sundial. The former represent the time and the latter the seasons. One can tell the time by observing the shadow on the lines made by the sun's movement as it rises from the east and sinks in the west. One can also see the 24 divisions of the year by observing the changes of shadow on the lines due to the different altitude of the sun at noon from season to season. One remarkable feature is that time is indicated for illiterate people by substituting the usual 12 letters on the plate with 12 animal guardian deities. In addition, such sundials were placed not only in the royal palace but also in public places such as Hyejeonggyo Bridge in Jongno and Jongmyo Shrine, which means that they were the first public clocks. Two sundials preserved in Changdeokgung Palace in the shape of a small concave iron pot with four legs boast a graceful figure. These two show the same style and technique, and can easily stand comparison with other works of art because of their delicate and unique mode of manufacture. The body of this one is made of bronze and painted black, and its letters and lines inlaid with silver. It has cross-shaped legs to keep its balance. This outstanding sundial of the Joseon Dynasty is a valuable relic and a scientific cultural asset.