The brass base is shaped for mounting on the gun, with the two sections of a silvered brass upright plate sliding in a slot in the base, with a central upright slot, and joined at the top by a shaped and pierced brass cornice. A rigid brass plumb-line is suspended to one side with a target. A brass sight with two pinholes moves in the upright slot, with indexes to either side moving against 2 scales. One is 0 to 3 1/4, divided to 1, subdivided to 1/2, 1/4, 1/8 and 1/16, numbered by 1, with the quarters also numbered 1 to 3. The other scale is 0 to 3 1/2, similarly divided and numbered.
