The Scheinergrade (Sch.) system was devised by the German astronomer Julius Scheiner (1858–1913) in 1894 originally as a method of comparing the speeds of plates used for astronomical photography. Scheiner's system rated the speed of a plate by the least exposure to produce a visible darkening upon development. Speed was expressed in degrees Scheiner, originally ranging from 1° Sch. to 20° Sch., with each increment of a degree corresponding to a multiplicative factor of increased light sensitivity. This multiplicative factor was determined by the constraint that an increment of 19° Sch. (from 1° Sch. to 20° Sch.) corresponded to a hundredfold increase in sensitivity. Thus emulsions that differed by 1° Sch. on the Scheiner scale were 100 19 = 1.2742... -fold more (or, less) sensitive to each other. An increment of 3° Sch. came close to a doubling of sensitivity ( 100 19 ) 3 = 2.06914... .