On the faces of the "superior casamento", as already said, take place the dials of each stars. To read the information about them it is necessary to remember a few elements of Ptolemaic astronomy .

As to Giovanni's explanations and as to your writer's understanding, the movement of stars accordingly to ancient astronomers was very complex.

They checked up that, besides their own possible independent motion, all planets and "fixed" stars moved incessantly in one direction and therefore thought they were part of a sphere which was called the "first mobile", which makes a rotation in one day on its axle .

This sphere revolved around an axle passing through the earth and having its own north and south poles. The closest the stars ware to these poles, the smaller was their revolution and , as a limit, the star positioned exactly at the north pole - the Polar star - was standing so firmly to be considered by sailors the reference point to trace their courses.

The planets moved in a band tilted by 23 degrees to the " first mobile" equator .
This "band" was called the Zodiac.

The Zodiac is made up by 12 constellations. The particular position of the stars of each constellation gives them their well known names . Ancient astronomers thought it was easier to explain the motion of the planet showing their position in the Zodiac.

Let us say the Ptolemaic solar system was very complicated.
To account of such a complex motion they figured out as the first simplification that planets revolved exactly along a circumference called "equating circle" (Figure 1).

Since planets actually moved along ellipses, the artifice used to reproduce such curves was to let the center of an other circumference - called "deferent" - to revolve along the "equating circle" (Fig. 2) along which, in turn, a point called center of the "epicycle" was also moving (Fig. 3 & Fig. 4).

fig.3		fig.4

The curve drawn up by the epicycle center shows the path made by the point around which the planet completes an imaginary revolution (Fig. 5).

	Figure 6 clearly shows how, to man (point A) standing on the earth, the planet P seems - during its imaginary revolution around D - to move quickly in section 1-2, to slowly come back in section 2-3, even faster in section 3-4 and to be slowly going forward in section 4-1. Giovanni was able enough to show these complicated motions. From a practical point of view to show the position of a planet in the sky we need therefore to arrange for:
fig.5		fig.6

	A) A dial (its center representing the center of the earth) with a band engraved by the names of the Zodiac constellations (Fig.7) B) A wheel making a turn in the time taken by the planet to make its revolution. Along one of the wheel arm is housed a cursor on which a pivot representing the center of the epicycle is fixed (Fig. 8). C) A disk, the epicycle on which is fixed a pivot depicting the planet (Fig. 9).
fig. 7		fig. 8
D) A pointer - free to rotate around the center of the dial (ideally the earth) -and moved by the pivot of the epicycle. It also has a line of faith crossing the Zodiac to allow the readings (Fig. 10).

fig. 9	What shown above is the very synthesis - with many simplifications - of what Giovanni De Dondi did to show the motion of the stars. Bibliography G. de Dondi - "Tractatus Astrarii"- ( Biblioteca Apostolica Romana 1960 )
		fig. 10