Consists of a white metal circular tray 12" (30.5cm) dia., the rim of which is graduated quadrantally and to 360 degs. A white metal rotatable disc 10.6" (27.5cm) dia. is set in the tray; it is inscribed with alternate red and black parallel lines and carries vertical and horizontal scales graduated 0-32 (horizontal scale having an arrow head at end). Pivoted at centre of instrument are three white metal bars.
One bar is graduated 0-28 7"(17.8cm) long has clamp at end operating on outer rim of instrument and is fitted with a white metal disc 3" dia. graduated 0-180, and which has a folding arm 9.5" long, graduated 4-50. The disc slides along length of the bar. The other two bars 6" long are graduated 0-30 and are fitted with a sliding index.
In a fitted wooden box 13.25 x 13.25 x 4" (33.7 x 33.7 x 10.1cm) and in lid of box is white metal bar 12.25" long and graduated 0-70.