mine works out to be a fairly constant 5% error, ie, 60mph = 57 actual - which has been confirmed many times by those roadside speed radars

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Mark _______________________________
2001 X5 4.4i topaz blue/sand Sport, complete Dinan S2 , hitch, V1, tint, BSW Stage 1, Alpine INA-W910BT
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Life is not fair!
You can't protect people from their own stupidity!
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