DMcQuinn,

You are correct. The Hall effect uses a small(3/16") magnet mounted on the spinner backplate. We tested optical, infrared, inductive, and Hall effect sensors. Without a doubt, the Hall effect is the most accurate with the least amount of electronics. Also the small magnets have been tested at 1/4" gap and still perform well. Our goal is to sell a premium instrument that is accurate and easy to mount/use. I think we have it.

i4c Products
Rod Johnson