This 1948 short film by Popular Science magazine screened in movie theaters before Paramount Pictures features. It shows a mechanical differential analyzer in use by UCLA engineering students and researchers.
"This amazing mechanical brain quickly solves mathematical problems that would require months by ordinary computing methods. The brain is becoming an invaluable aid in our aircraft capital — speeding engineering research and reducing time spent on flight tests. It is also available for solution of other industrial design problems."
Posted at Paleofuture on the web.