What shape is a sundial? What are the components?

The sundial is a square slate with a deep round hole in the center, a big circle around the round hole and 69 shallow holes engraved on the circumference. Shallow holes are marked with numbers from 1 to 69, and there is a straight line connected with the central circular hole. According to the estimation that 69 holes occupy a little more than 2/3 of the circumference, the whole circumference is divided into 100 on average, and each shallow hole accounts for1100. Judging from the font used, it is a relic of the Qin and Han Dynasties.