On my Glory, the error factor doesn´t seem to be linear. e.g., if I´m going 20 m.g.h. on the speedometer, my actual speed is 16 m.p.h. (20% high). But at 72 m.p.h. on the same speedometer, my actual speed is 63 m.p.h. (12.5% high). That´s using gps or a chase vehicle. Also, when I first got my bike, the odometer was actually tracking kilometers instead of miles. When I did my first oil change and reset the error code it started tracking miles. My trip to work changed from 35 (km) to 22 miles. All part of the fun of getting to know the machine.