Found something really weird today… a 10-foot tall calculator…. made entirely out of K’NEX.

No digital display. No abacus. Just K’NEX:

The thing works by dropping nine balls into the top of the unit. Four balls for the first number (that’s binary allowing up to the number 15), one ball for the operation (add or subtract) and four balls for the last number. The balls then drop through a series of tracks and logical gates to calculate a final answer.

The most interesting part is how they duplicate the logical gates by controlling how the balls flow. A normal logical gate, say an AND gate, only will produce output when both inputs are true. So they figured out a way to make a physical AND gate drop the ball only when two balls are input to the gate. This is how they got a completely mechanical, non-electrical unit to do such calculations. Yes, this is how we did it ages ago, and really how we learned to do what we know as computing today.

But for a hopeless geek like me, this is crazy cool.