NEW VERSION!!! POSTED 12-29-13
At first glance the updates are barely noticeable, but every piece has been revised. The changes make assembly easier with better fit and smoother operation.

This Math manipulative is designed to appear playful from the first look. It lies flat on desk top, so it will also work well with overhead projection systems.

Behind the mechanical fun there are several simple ratio exercises. The eight tooth "Idler" gear is supplied to add reverse rotation without affecting the ratios. Each interchangeable gear has built-in graphics to indicate the number of teeth as well as rotation position. Some gear ratio formulas can be found here: http://en.wikipedia.org/wiki/Gear_ratio.

Rubber bands provide tension to keep the wheels engaged no matter what the combination.

FYI, the "T" on the gears stands for "teeth".