This portable sundial, made in the shape of a triangular prism and calibrated for a latitude of 42?, corresponding to Rome, bears the hour lines traced on its faces. A compass, to allow the instrument to be correctly oriented for reading the time, is located in the base.
Although the instrument is unsigned, it could be the work of Girolamo della Volpaia, the son of Camillo and a maker of observational and measuring instruments for the Medici dynasty.