With the camber roller assembly, you can easily and accurately introduce a slight camber when sharpening your plane blades. That way, you can avoid those lines you see when flattening a surface with your hand plane because each stroke will blend into the last. Just swap out the stock roller on your Mk. II Honing Guide with the camber roller and you're good to go! The camber roller includes the same eccentric system to quickly adjust for micro bevels.