"The Compound Protractor" - a Station Pointer fitted with an Alidade
Material: Boxwood and brass.
Boxwood rule: 12.5" (31.8 cm) long, 1,6" (4.0 cm) wide. One edge is bevelled and graduated to 12" by 1/10s
Protractor: Brass 2.5" (6.4 cm) radius attached to boxwood rule at centre of unbevelled edge. Graduated 90 - 0 - 90 degrees, 0 - 90 - 0 degrees by 1 degree
Arms: Three brass arms 6.5" (16.5 cm) long are pivoted on a short brass tube, with clamp screw, at centre of radius of protractor. The arms are of open frame form with threads at centre.
Shadow pin / Chart pricker: Steel 5.25" (13.3 cm) long. Can be inserted in the short brass tube at centre of radius of the protractor.
Alidade: Brass 5.3" (13.5 cm) long, fitted with two sight vanes, one an open frame with a thread, the other a slit with dark glass share in a sliding brass frame, can be fitted on the same mounting as the shadow pin.
Fitted woodenbox 13.25" x 5.02" x 2.26" (33.7 x 12.7 x 6.7 cm) containing a Xerox copy of the registered "Design Office" drawing of the instrument dated June 3, 1862