Before using the instrument, it is necessary to place the circular quadrant parallel to the plane of the celestial equator of the place of observation so that the local celestial meridian intersects the quadrant along the line from hour XII to hour 0. To do this it is necessary:

a)      to level the wooden base using an air bubble level and turning the levelling screws, rotating the small base so that the 0 of the circular scale joined to it, as results on the side of the foot of the staff, coincides with the direction of the needle of the compass; in this way the meridian plane of the place will intersect the small base passing through the line of the zeros, which represents the direction of the cardinal points North-South, and then through the foot of the staff;

b)      to free the main hinge of the circular quadrant and orient it so that it slopes with respect to the plane of the base by an angle equal to the colatitude of the place (for Cagliari the geographic latitude is 39°15', and thus the colatitude of 50°45'). Thus the circular quadrant will be parallel to the plane of the celestial equator and will be intersected by the plane of the local celestial meridian according to the hourly line of hour XII. ...continues