Henry Seton-Karr and Charles Francis Atkinson, 1911 Encyclopædia Britannica (1911)
“ At the School of Musketry, Hythe, the standard of judging distance is “not more than 100 yds. wrong at any range.” Now at 1000 yds. an error in judging distance of 13 yds. above or below the true range will cause all the shots of a particular rifle to fall away from the target, and the better the marksman—i.e. the closer his group the more necessary is perfection in judging distance, a perfection which in reality seems unattainable. The British musketry regulations therefore lay it down that the individual marksman’s fire at service targets is unprofitable at ranges of more than 600 yds. ”
