Mine will occasionally indicate I'm riding at half speed. Like I'll be tooling along at 18 MPH and then it will briefly flash 9 MPH and then right back to 18. So I assume the odometer function is also only measuring half the distance for that short period. Probably not a big discrepancy but over a 10-20-30+ mile ride, I wonder how much it is off by? A half mile? A tenth? Too little to matter? I have no idea.

If I remember to do so, I might relocate the sensor up or down on the fork and see if its angle vs. the magnet makes any difference.