Sir David Salomon was granted a patent number 3615 on 8 March 1888 which 'relates to a slide-rule specially graduated to calculate the rapidity of photographic lenses'. Although Coe describes the H & D Actinograph as being 'the first in a long line of slide-rule type calculators' Salomon's device would appear to predate it by one month. That said, the Actinograph was unquestionably the more scientifically determined and influential of the two calculators.