>>1603581It's much simpler than you think, I think. Just like a traditional bike speedometer, it just uses magnets. The sensor is in the chainstay as you noted, and you use a magnet on the crank arm for cadence and a spoke magnet for speed. Cadence is just RPMs, obviously, so it calculates that easily. For speed, you program the tire size so it knows how far you've roller per revolution of the wheel. Make sense?