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細節
A 19th-Century lacquered-brass swinging arm protractor,
signed Troughton & Simms LONDON., with two swinging arms with steel points and blued-steel springs to the hinges, a glass with engraved cross hair at the centre, each arm with a silvered vernier to the toothed silver circumference scale, moved by means of a wormgear turning knob, in the original fitted mahogany case with one brass hook and two eyes (one hook missing) -- 6¾in. (17cm.) wide
See Colour Illustration
signed Troughton & Simms LONDON., with two swinging arms with steel points and blued-steel springs to the hinges, a glass with engraved cross hair at the centre, each arm with a silvered vernier to the toothed silver circumference scale, moved by means of a wormgear turning knob, in the original fitted mahogany case with one brass hook and two eyes (one hook missing) -- 6¾in. (17cm.) wide
See Colour Illustration