Lee
Basically I measured the car speedo indicated speed against a couple of satnav devices. Then I entered into the speedo calibration mode, done by holding done odometer reset button then turning ignition on. Basically I then increased the speedo pulse number by close to the percentage of the over read. After a bit of trial and error I arrived at a speedo that reads roughly 1% fast, as opposed to 10% before. The final number of pulses can be + or - a bit since you're looking at a high number.
Mine is now set at 24670 but I have a km/h speedo so the number needed in your case may be different? I'm sure your dealer will know
Cheers
I'm sure your local dealer will
