You need to drive a measured distance, compare what the Raven says it drove to the tape measure. I like at least 500ft. If it is off more than a couple of feet then plug the numbers into the equation in the operators manual.

New cal# = (old cal X distance from tape measure) / distance on console

The same equation can be used for flowmeter calibration IF you can accurately measure the output. Possibly pump water into a minibulk tank.

The gps speed on the cruiser may not be the same as the calibrated controller speed.