T. F. Randolph termed this a Patent Vernier Telescope Compass, referring to his 1879 patent (#216,769) for an Improvement in Surveying-Instruments. The raised rim is silvered and graduated to single minutes. The variation arc, located on the compass face, extends ± 20 degrees and reads by double vernier to single minutes. There are two level vials on the face. The telescope assembly is provided with two obviously later additions: a level vial marked "G. F. RICHARDSON, ATHOL, MASS." and a vertical arc marked "G. F. Richardson, Athol, Mass." and "PATENTED Aug. 16, 188x."
Ref: T. F. Randolph, Illustrated Catalogue and Price List (Cincinnati, 1892), p. 2.