The case of the clock is richly decorated and ornamented. Above the dome is an armillary sphere which can be manipulated by hand. The rings are graduated and inscribed with the names of the constellations and the winds. At the centre of the sphere is the earth. The celestial meridian bears the hour circle, and a small compass is contained in the base.
The faces of the clock display numerous circles designed for a wide variety of uses. The larger circle is the plate of a mechanical astrolabe, with an hour circle numbered twice from I to XII, and completed by the rete and pointers for the sun and moon. The plate is reversible, with one side calibrated for the latitude of 48( (Bavaria, Vienna), and the other side calibrated for 40? (the Madrid area). Under the rete is the pointer for the nodes, in the shape of a dragon.
The abbreviation 'CR' has been inscribed twice on the back of the quadrant with the astrolabe. This signature can also be found on other clocks of great beauty and complexity. Although we cannot be sure of the identity of the instrument maker, the abbreviation might possibly stand for Cristofor Crofler, who made a clock for Maria Cristina di Lorena, the wife of Ferdinando II de' Medici. This attribution is not supported by any strong evidence, however, and does not seem to be especially probable.
See G. Brusa, 'Origine e definizione dell'orologio meccanico", in M. Miniati Museo di storia della scienza: Catalago, (Florence, 1991).