### The Difference Engine

You must check this out:

Before the day of computers and pocket calculators all mathematics was done by hand. Great effort was expended to compose trigonometric and logarithmic tables for navigation, scientific investigation, and engineering purposes.

In the mid-19th century, people began to design machines to automate this error prone process. Many machines of various designs were eventually built. The most famous of these machines is the Babbage Difference Engine.

Babbage's design could evaluate 7th order polynomials to 31 digits of accuracy. I set out to build a working Difference Engine using LEGO parts which could compute 2nd or 3rd order polynomials to 3 or 4 digits.

One may well ask what possible point there could be in building a mechanical calculating machine using a 19th century design and 21st century plastic toy blocks. The only possible answer to that is -- hey, it's a lot easier than those heavy metal discs that babbage originally had in mind. Besides, it's important that we understand mechanical computers. They're the wave of the future.

Bonus: the page has lots of good background on how a difference engine works.

Via GeekPress.