Graphometer with a compass at the centre. One movable arm marked 'alidade mobille'. The base is marked 'alidade des stations' and has left and right sides marked as 'Partie fenestre' and 'Partie dextre' respectively. The moveable arm can be put at right angle with the base, allowing for measurement of right angles.
Graduations-Semi-circle graduated 0-90-0 by 30'. The alidade 10.8" (27.5cm) long has one edge bevelled which acts as a fiducial edge. There is a straight edge 11.25" (28.6cm) long on the lower part of instrument. A tripod mounting cup with articulated joint is attached to back.
Sights-Two folding sight vanes 1.1" (2.7cm) long mounted on straight edge, both sights have a peep-hole with a slit above. Two folding sight vanes 0.9" (2.3cm) long mounted on alidade, both sights have a peep-hole with a slit above.
Compass-Dia. 1" (2.6cm) mounted at centre of alidade. Fitted with a blued steel "arrow" shaped needle with a brass pivot cap at centre. Graduated to 16 points.