Clock of Chiaravalle

During his stay in Milan, Leonardo devoted many drawings to the study of sophisticated mechanisms for the planetary clock at the nearby abbey of Chiaravalle.

In this model, the moving organ is located inside a wooden structure, where a weight lowers, causing a drum to turn, setting into motion a series of shafts and toothed wheels that carry out ordered sequences of movements.
The internal mechanisms correspond to three clock faces on the outer structure: two smaller ones, for counting the minutes and hours; while on the largest, with its 12 zodiacal divisions for the year, dedicated moving hands show the positions of the sun and moon and the lunar phases, as well as other astrological and astronomical indications.