I just came across this product, which is an optical mouse that you strap to your finger. What made me think about robotics is the possibility that it may be more tolerant in regards to the distance to the ground. The pictures clearly show it being used so that the mouse is at least 1/4" from the surface. However, people who make advertisements have been known to produce pictures that have nothing to do with reality. I have not personally tested or even seen this product. Cost $20
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Joe Dunfee