An electronic measuring device is disclosed which includes a pair of wheels connected to an axle that passes through a drive gear. The drive gear is enmeshed to a second gear which, in turn, is coaxially connected to an encoder disk. The encoder disk has spaced-apart fins around its outer periphery....http://www.google.ca/patents/US7036241?utm_source=gb-gplus-sharePatent US7036241 - Rolling electronic length measuring device
