Speedometer Problem

Hello all my name is Darius
I have a: (GTO, 3000GT, VR4, TT) 1991
It has the following issue: problem with the electric speedometer, after turning on the ignition, the speedometer already shows 30 miles, even though the car is stationary. when driving, it shows the wrong speed. what can I do , to fix it? thanks

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Remove the cluster and the clear plastic cover, refit to the car and on a long clear closed road or better a dyno, get to 30mph via GPS (google maps) or on the dyno speed and then pull off the needle and refit as accurately to 30mph as possible. You can’t set the speedometer to be accurate at all speeds (it will usually always read higher than actual road speed) so best to set it accurate to 30mph and not worry about being over any speed limit.