3 chevrons is the max. 1 chevron is 4 -6% grade (and I think it has to be sustained over at least a half mile to a mile to earn a chevron), 2 chevrons is 6 - 8% and 3 is 9%+, so once you get over 8% it's not very exact. They are VERY cool, though, and quite helpful. If you want one, they have Krebs maps at a lot of cycling stores, or you can purchase them online at www.krebscycleproducts.com.