This instrument is similar to Gurley’s small vernier compass, but it has no vernier mechanism. The outer rim of the box is graduated to single degrees, and numbered every 10 degrees. The instrument can either be used with the folding sights raised to the vertical, or with the sighting bar. In the latter case, the folding sights are be folded towards each other, to form a tent, and the sighting bar attached on top. The sighting bar is equipped with a vertical circle graduated to single degrees. This form has not been found listed or described in any Gurley trade literature. However, since the signature was engraved by machine, it must have been made after 1876.