A mariner’s astrolabe with a cast brass frame, but missing the alidade and suspension ring. Part of the axial pin is jammed in the pivot hole. The mater has been made from a single casting with the bottom ballast, which is wedge-shaped. This is to assist the instrument to hang the plumb in the vertical plane during an observation. The device is badly eroded.

There is a small star-like mark on the face of the bottom ballast, which has a thickness at the top of 14 mm, at the bottom 28 mm, and a weight of 3288 grams.

Several digits of the scale are visible indicating a graduation on the upper half of the frame, on either side of 0° at the top: a division of 90° to 0° to 90° numbered to 5°, but the graduations are obliterated.

Found in Mounts Bay, Cornwall, in 1982, purchased from the Receiver of Wrecks, H.M. Customs and Excise, Customs House, Penzance, Cornwall, in 1989. A Spanish escudo of about 1520 found at the same site suggests that the astrolabe may have been made in Spain. However, it is also similar to an illustration in William Bourne's 'A Regiment for Sea' (1574).