Instead of matching speeds, wouldn't it be better to do a DISTANCE test? I don't know, are section roads 1 mis x 1 mis (or relatively close) in ND? If so, then just take your sprayer tractor out on a road & drive for 1 mis w/the radar. First make the distance read 000. If your calibration is correct, then you should come up with 5280' (or whatever your section miles are). If not, there's a formula given in Raven manual for recalibrating the speed cal #, which is really measuring distance & applying a mathematical formula internally to read out mph to you. If you're only off by 5-10', I wouldn't worry about it. But, if you have time, you can re-cal. This method could/should be used with both radar & gps. But, you have to have a distance (feet) to work a calibrate speed formula.

That's how I'd do it...and have done it.