The Sun's Altitude
This altitude depends on the latitude, and also varies throughout the year; maximum altitude occurs during the summer solstice and the minimum altitude occurs during the winter solstice. At the latitude of Valencia, the maximum altitude reached by the Sun during summer solstice is 73º 57’; during the winter solstice it only reaches 27º 5’.
If you look at the shadow of the indicator rod at 12:00 solar time, you can obtain the solar declination for today's date. The declination is the angle between the Sun and the celestial equator. As the declination of the sun varies according to the day of the year, the plinth can also be used as an accurate annual calendar –but only at exactly solar noon.
The plinth can be used to determine when the solstices and equinoxes will occur. To do so, all you need to do is read off the mark indicated by the shadow at solar noon.