This circular instrument was crafted to sit atop a U.S. Navy Standard Compass and manufactured in Brookline, Mass. by E. S. Ritchie & Sons, Inc. and includes its original wooden box.

Featuring dual sighting mechanisms, this device serves multiple navigational purposes. One method involves sunlight, reflected from a cylindrical convex mirror onto a right-angle prism situated across the ring, then through a cylindrical lens below, manifesting as a luminous bar on the card. Alternatively, it employs sight vanes, hairline, and reflector for determining bearings of terrestrial objects.