My speedometer on my golf 1.4 seems to be incorrect as last night when i was on the motorway the clock sed i was doin 60mph but i was flyin past everyone on there.Also i had a garmin satnav on the go and when u reach the speed limit it beeps and each time i reached 60mph the garmin was beeping assuming i was at the speed limit. How can i go about getting this fixed?and does anyone kno how much it would cost to get done.