A rare late 18th Century lacquered brass graphometer,signed on the main frame J.L.Koch Fecit Berolini and dated 1762, the rotating alidade with two folding sights, with securing points for the compass (missing), finely engraved with stylised foliage, the scale pointers on curved links, the main frame with two folding sights similarley engraved, scales for Umbra Recta and Umbra Vensa well divided, the outer scale 0°-180°, the inner 180°-0°, both with subdivisions, on universal ball and socket staff mounting with twin 'butterfly' tightening screws - 11½in(29.2cm)diam