You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Film_speed

Context:
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.

Question:
What is the range of Scheiner speeds?

from 1° Sch. to 20° Sch