My ST1300's speedometer is woefully inaccurate. According to my GPS's, it under reads by around 5km/h to 10km/h (the faster I'm going, the greater the error). If I never go over the posted speed limit (according to the speedometer), I don't think I would ever get a speeding ticket.
The under read is within ADR specs for a speedometer as annoying as it maybe.
http://www.racq.com.au/cars-and-driving/safety-on-the-road/driving-safely/speedo-accuracyAfter 1 July 2006
From 1 July 2006 all newly introduced models of a vehicle available on the market must comply with ADR 18/03:
•The speedo must not indicate a speed less than the vehicle’s true speed or a speed greater than the vehicle’s true speed by an amount more than 10 percent plus 4 km/h.
•The speedo must always read 'safe', meaning the vehicle's true speed must not be higher than the speed indicated by the speedo. So if a vehicle travelling at a true speed of 100km/h, the speedo must read between 100km/h and 114km/h. Another way of looking at this is if the speedo indicates a speed of 100km/h, the vehicle's true speed must be between 87.3 km/h and 100km/h.
•There is now no requirement to have an odometer, and so there is no accuracy requirement
My current TomTom GPS gives me a speed of 97 K/H for an indicated 100 and 105 K/H for 110.