Transparent celluloid rectangular instrument. At one end is a radial protractor scale 0–90–0–90–0. Along the centre is a 125 mm slot with one end at the centre of the protractor scale and of width to accept a pencil point, with scale divided into tenths.

Inscriptions:
The Leanthall Course Delineator
Patent No. 12631 09
Heath & Co Ltd London

Contained in a mahogany box with sliding lid, with receptacle for a pencil. The box also contains a folded sheet of paper with pencil marks.

Instruction book: 98 x 150 mm booklet of 32 pages in red paper covers, giving instructions for various navigational tasks.