Babbage's Difference Engine No. 2, Part 3: Interlocks

In the 1840's, the English mathematician Charles Babbage designed his "Difference Engine No. 2", a special-purpose mechanical computer for constructing mathematical tables using the method of finite differences. The machine is massive, weighing several tons, and was not actually built until 1991. This multi-part video series explains what the Difference Engine No. 2 does and how it works.