A quality mahogany cased brass rolling parallel rule by Troughton & Simms c1890. Period instrument of solid brass construction with attractive aged patina. In original fitted mahogany case with pinned dovetail corners - an indicator of the quality of construction. These were supplied for technical drawing or navigational purposes. Upper side to baseplate stamped Troughton & Simms London. The rule is 46 cm in length and 7 cm in depth. Case measures 49.5 cm by 10 cm and 4.25 cm in height.
 
Troughton & Simms was a British instrument-making firm formed when Edward Troughton and William Simms entered into partnership in 1826. Edward Troughton (1756-1835) had learned his trade from his uncle, John Troughton, a leading instrument maker in London – and had also worked with his equally talented brother, John Troughton (1739-1807). William Simms (1793-1860) apprenticed under a Mr. Bennett, a London based mathematical instrument maker of considerable ability and reputation. He subsequently started a business on his own making theodolites for the Board of Ordnance. Troughton & Simms produced high quality astronomical instruments and drawing instruments used around the world. In 1876, they supplied the Imperial Standards of Length gauges mounted at Trafalgar Square in London UK. The company became a limited company in 1915, trading as Troughton & Simms Ltd, and in 1922 merged with T. Cooke & Sons to form Cooke, Troughton & Simms (which became a subsidiary of Vickers in 1924). In 1963 the company became part of the newly formed Vickers Instruments which continued until 1988.