This dial is known as a naviculum dial because is shaped like a small boat. Of this type of instrument, documented from the fourteenth century, only a small number of specimens have survived. The dial consists of two engraved brass plates joined together. The front displays the lines of the diurnal and average hours, and a zodiacal scale (lower center). The rod hinged at the center can describe an arc of about 45° and is partly covered by the two plates, while the lower protruding end can serve as an index. The rod has a cursor to which is attached a string with a small weight (now missing). The back carries the shadow square, the lines of unequal hours, and a 90° scale. The months shown by the index are displayed at the bottom. Provenance: Medici collections.