This instrument is made up of two legs which are curved near the ends. The curved parts contain a degree scale on one side and a Cardan suspension compass on the other. The compass is equipped with an equinoctial sundial.
The legs are pierced with holes which allow the passage of a ray of sunlight, allowing the sun's elevation to be measured with the aid of a plumb-line, which is now missing. A second graduated arc provides direct-reading gunner's gauge scales; when the legs are opened to measure the diameter of cannonballs the arc provides a reading of their weight.
The lion of St. Mark, alluding to Venice and the Venetian Republic, and the name of the inventor, Lorenzo Batecin, about whom we have no information, are engraved on the instrument.