First lesson of the day, speedometer needles are magnet driven, odometers are gear driven.
The magnet can be dirty or weak and make the speed wrong.
Odometers are gear driven off the cable and gears. Tire size, rear axle, and speedometer gears will change the odometer.
Odometer should be corrected first, then address the speedometer.
Drive ten miles at a steady speed on a marked highway and write down the mileage shown compared to marker signs.
Adjust gears or add adaptor to correct the odometer.
Speed doesn't matter to the odometer.
https://www.speedoservice.com/speedometer-calibration/ These guys can fix you up with parts or service.
Speedometers / odometers are calibrated to 1000 rpm cable = 60 mph.
