Coincidence Rangefinding (Civ6)/Civilopedia

In the 1880s, the British Admiralty – recognizing the improvement of naval guns and ammunition – issued a requirement for a new rangefinder accurate to 3% at 3000 yards. In 1888, professors Archibald Barr and William Stroud built the first coincidence rangefinder that did just that; by 1898 their firm had sold over 150 around the world, most fitted to battleships. The device consisted of a long tube with a forward-facing lens at each end, two prism wedges inside, and an eyepiece in the center; The operator can rotate the prisms until the two images align; the degree of rotation of each will then give the range to a distant target by simple triangulation. Coincidence rangefinders became the naval standard ... until replaced by modern laser rangefinders.