I know that my speedo is definitely off which I can live with. When I measured the distance with my GPS I noticed that when my odometer hit 0.5 miles the GPS indicated 1 mile traveled. At first I though, oh great but then noticed at every 0.5, 1.5, 2.5, 3.5, 4.5, 5.5 etc my odometer read, the GPS went up one more mile traveled so I'm assuming as long as both increase at the same point every time, the odometer is calibrated correctly. As long as my odometer is accurate I am happy. I am just worried that if my speedo is off that would throw off my odometer too.