I almost hate to say this but when all else fails read the directions. Sorry couldn’t resist because I’m famous for not reading them. I can’t specifically give exact procedure but in settings somewhere is a calibration or variable setting to modify the count to make the speed correct. Also make sure the gps and the units are all in knots or mph. The only problem at this point is Raymaine is red back lit and Text display is blue gonna have a freakin rainbow on my dash. Also did not get a desired oil sample report on Starboard engine, so I resampled it just in case I contaminated the first one.