In NZ there are specific stretches of road accurately marked for odometer (not speedo) calibration. The speedo reading and odometer accuracy are NOT necessarily linked so using the 100m markers in UK is not going to help unless you also use an accurate stopwatch. An under-reading speedo is a liability for many reasons.
I understand most of the current trads can have the speedo calibrated by the user (there is some sort of menu that can be accessed by a button press though I don't have the details) - someone on here will know how.
