11 hour lines engraved on a semi conical concave surface with an inclination towards the celestial pole, arranged at distances of 15º defined the 12 day hours, while the three curves defined the path of the Sun during the summer solstice (the lowest line) the equinoxes (the central line) and the winter solstice (the upper line). On other days, the shadow of the Sun outlined parallel arcs between the curves, according to the season.