A 'compensated' pocket barometer altimeter by Ross, London, circa 1870, 2” silvered dual concentric engraved dial with rotatable altitude scale, the inner dial calibrated in inches/Hg, the outer with an altitude range from 0-10’000ft, the dial centre marked 'Compensated', signed by the maker 'Ross, London' and numbered '973' fine blued-steel pointer set beneath bevelled glass, machined bezel to a flat finished brass case, stem with suspension loop, lacquered brass conventional movement with bimetallic compensation to secondary lever, the case rear with compensation port set at 4 o'clock, pin original, burgundy, embossed patent Moroccan leather-covered case with cream silk and imperial purple velvet lining.