Photostats Model Sheets were extremely important in the making of an animated film. The term photostat refers to the copying process which was used at that time, usually a photographic or Printing Process. Photostats were made from original model sheet drawings showing the characters in many poses. Once Produced, the photostats would be given to the various departments to insure consistency among all of the animators working on a project. The number of photostats needed would vary with each production. They represent a wonderful window into the production process of an animated project.
These photostats and and their description are from the Van Eaton Galleries website.