The rim of this compass is graduated to 30 minutes. The variation arc on the south arm extends 20 degrees either way, and is read by folded vernier to 2 minutes. There are two level vials on the north arm, and an outkeeper on the south arm. The side of one vertical sight is graduated to half degrees, for determining angles of elevation or depression. The machine-engraved signature indicates a date of manufacture after 1876. This instrument belonged to Columbia
Ref: W. & L. E. Gurley, A Manual of the Principal Instruments Used in American Engineering and Surveying (Troy, N.Y., 1904), pp. 108-120.