I've had a buddy come over a few times and put his bike on the imagic to do some courses. He has a powertap hub and the few times he's been over, the imagic read between 15-30 watts more than his powertap showed. So mine isn't too far off at least up to 400 watts, but then again, I guess I don't know how far off Rok Kolars imagic may be off. From what you guys have reported maybe it is way off. Still, this guy pulls away from me at a pretty good rate. I can hang with him for 6 to 7 minutes and I just plain can't hang on any longer.