Variance between Gryphon and actual milage

[p40whk]

Thanks for the quick replies, I'll add the circumferences tonight.

I wasn't sure what was more accurate since my speed on the Gryphon reads about 3 mph slower than what my dash needle shows. I would imagine the Gryphon is what's accurate since I regularly go by police with my truck in cruise control set 9 over and have never been pulled over. When my Gryphon shows me going 79 my dash gauge says I'm doing 82. Since the readings are coming from the computer and not converting the speed to an anolog gauge I am assuming that the Gryphon is more accurate. I hope I'm right! Otherwise I may get pulled over real soon!