... or "what use is a cardboard computer?"

This page is about a fantastic, old computational device called a Cardiac

Cardiac stands for Cardboard Illustrative Aid to Computation.

More details are available on the Wikipedia Article and the Google+ Group. There are plenty of articles around which explain how this device works, including this one from Hackaday. There was also an ultra-rare teachers version which came on acetate so it could be used on an overhead projector - noice :)

The CARDIAC manual is a fantastic read if you are into Computer Science history in general and has some brilliant 1960s illustrations. Also, if you ask your teacher, they may have an original one to show you! If not, you can still buy them from Ebay. They also came with a Teachers Guide but they are as rare as Hen's teeth.