I downloaded an app to my smart phone that lets me get my speed , direction , and trip miles. On my Thruxton I am 7 mph off . For example when the speedo reads 60 , I am going 53 . At 70 , a real 63 . So , If I am on the super slab and I need to stay with traffic say a real 75mph , My speedo must read 82 . NOW for the Norton 961 , a mere 2 mph off. That's car good ! So when I am going 80 a real 78 mph shows up on my phone! That's a good calibration folks .