Deux instruments de calcul pour l'étude des cartes : - NEGRETTI ZAMBRA, Opticians, London Brass protractor circle engraved around the rim with scales and Arabic numerals. Signed on the central edge. Diameter: 30.5 cm. Some cast defects and wear scratches. In its mahogany case (scratches). - H. HUGHES & Son, London Bronze stigmograph with three extendable rulers. Signed and numbered 2772. Length: 67.2 cm. Wear, scratches and minor knocks from use; a few stains. In its stained wooden case (average condition without closing hooks; stains, scratches, bumps). Instrument used by hydrographic services to survey nautical charts.