OK-then there's something new. That "proximity sensor" just reads off of anything? There was a sensor (switch) that read off the magnets.

Have you not been able to calibrate either speed or flow meter to make things come out right? They should be 2 separate issues. What I usually do to calibrate gs part is to drive a mile (5280') to calibrate distance (g.s.). I know the book talks about 400', but seems to me that 13x that distance ought to even out the bugs a little. Ravens gives formula in manual for calibrating distance (gs).

Flow meter gallonage can be a little trickier. You have to come up with some type of known gallonage. I think plastic tank mfg warn that they can have up to 10% variance in their markings. Also-one has to consider whether the tank has been drained 100% wheni it's empty. Usually not. Ravens gives formula in that manual for calibrating flow meter also.

Sounds like you're only 6% off in gallonage (flow meter). GPA will be a combination of distance & flow....or their errors. Actually-one error could nullify another. After calibration-the only thing that could throw off flow would be something obstructing the flow meter turbine wheel or air bubbles. I guess your proximity sensor could be picking up something else also?

Good luck there.