Graphometer. See NAV1416.1 for part of the graphometer.
Graduations-Semi-circle graduated 0-180, 180-0 and carries a diagonal scale. The alidade 15.5" (39.4cm) long has a fiducial edge at each end. There is a straight edge 16.7" (42.4cm) long at lower part. A ball and socket head and a square plate 5.25 x 5.25" (13.3 x 13.3cm) is attached to back of instrument.
Sights-A telescope 25" (63.5cm) long, dia. 1" (2.5cm), erect with cross wires, mounted on alidade. A telescope 23.9" (60.8cm) long, dia.1" (2.5cm), erect with cross wires, mounted on underside of straight edge.
Compass-Dia. 3.9" (10cm) mounted at centre of instrument. Fitted with a blued steel needle in form of an arrow 3.25" (8.3cm) long, with a brass pivot cap at centre. Graduated to 8 points and to 0-180, 0-180 degs.
The addition of a telescope with cross-hairs enables a more accurate reading to be taken rather than with simple plain sight. This instrument is designed to only make horizontal measurements and has a compass for correct positioning.