The instrument, made entirely of brass on a square wooden base (17 x 17 cm) with four levelling screws, is essentially an equatorial solar quadrant (or solar clock) made up of the following parts:
- a magnetic compass enclosed in the base which can be freely rotated with respect to a circular dial subdivided into four quadrants, each graduated from 0 to 90;
- a circular quadrant supported by a staff fixed to the base, with a joint that may be blocked and which allows the quadrant to be inclined from 0 to 90 degrees with respect to the base; the quadrant is ideally subdivided clockwise into 24 hours (each division representing 4 minutes), but in reality the subdivision is in the interval from hour III to hour XII and from hour 0 to hour IX, which corresponds to the maximum duration of the day at latitudes in the temperate zones;
- a smaller quadrant, graduated from 0 to 90 degrees (each division equal to half a degree) and hinged under the circular quadrant which bears on the upper side the words Elevatio Aequatoris, and which, thanks to a system of freely moving hinges, always places itself in a vertical position, and a small weighted wire that almost touches it allows the reading of the inclination of the plane of the circular quadrant with respect to the plane of the wooden base.
A rod (with a notch at one end and a peg at the other) is fitted above the circular quadrant; this holds a staff fitted with a second staff (alidade) at opposite ends of which there are a small converging lens and a small screen with a small circle etched at the centre; the alidade can freely rotate 360 degrees parallel to the plane of the circular quadrant and about 30 degrees perpendicularly to it.


Bibliografia:
Daumas (1953), p.335
de Clercq (1984), p. 142
Turner (1987), p. 223


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