generate questions: 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., where an increment of 19° Sch. corresponded to a hundredfold increase in sensitivity, which meant that an increment of 3° Sch. came close to a doubling of sensitivity.
Who created the Scheinergrade system? {sep_token} What is the Scheinergrade system used for? {sep_token} What do degrees Scheiner indicate? {sep_token} What is the range of Scheiner speeds? {sep_token} Approximately how many degrees indicate double the sensitivity? {sep_token}