This sundial cast in bronze is originally called angbu-ilgu (仰釜日晷), literally meaning a “sundial resembling a cauldron”. It consists of a gnomon pointing towards the north, and a concave dial plate with silver inlaid lines indicating hours, and 13 horizontal declination lines for 24 subdivided seasons. The outermost declination line marks the winter solstice and the innermost line the summer solstice, because the shadow length expands in winter and shrinks in summer.

There are a total of seven hour lines, from sunrise in the hour of the rabbit (5:00-7:00a.m.) till sunset in the hour of the rooster (5:00-7:00p.m.), and short lines between each hour to indicate gak, a unit for 1/8 of an oriental hour which is almost equivalent to today’s 15 minutes. The concave hemispheric design for a sundial was invented during the reign of King Sejong (r. 1418-1450) and installed at the court and in busy streets as public timetellers. The Annals of King Sejong records that in consideration of illiterate people such sundials bore images of the twelve zodiac animals in place of hour marks.