A brass plate 5 x 5" (12.7 x 12.7cm) on which a spirit level in brass casing 4.8" (12.3cm) long is mounted. A fixed curved brass arc, graduated 0-90 degs is attached at side of plate. A second plate 5.25" (13.3cm) long is hinged above the first plate. It is fitted with a sight vane at each end 1.4" (3.6cm) long, one with a hole and cross threads, the other with a peep-hole sight. The upper plate is fitted with a brass clamp with fiducial edge whrough which the curved arc passes.




In fishskin covered case lined with red velvet.