Engraved on the surface of a hollow hemisphere 11 hour lines (arranged at distances of 15°) which were engraved on the surface of a concave hemisphere, defined the 12 hours of the day, while three curves defined the path of the Sun according to the summer solstices (the lowest line), the equinoxes (the central line) and the winter solstices (the upper line). On other days, the shadow trace from the vertical gnomon top (oriented to the South) outlined parallel arcs between the curves, according to the season.