I posted the rules in an earlier post. The new rules aren’t retrospective.
Australian Speedo accuracy standards
Australian Design Rule 18 sets out the accuracy standards for vehicle speedos.
Until July 2006 this rule specified an accuracy of +/- 10 percent of the vehicle’s true speed when the vehicle was travelling above 40km/h.
That is, at a true vehicle speed of 100km/h the speedo could indicate between 90km/h and 110km/h.
An odometer accuracy of +/- 4 percent was also a requirement.
From July 1 2006 a new standard began its phase in and by 1 July 2007 all new vehicles had to comply. The new standard requires that:
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.
Odometer accuracy is no longer defined.
What this means:
For a vehicle travelling at a true speed of 100km/h, the speedo must read between 100km/h and 114km/h. The effect of this is that many drivers will find that at 100km/h they are driving up to 14km/h below the speed limit if they rely on the vehicle’s speedo.
The speedo must always read 'safe', meaning the vehicle must not travel faster than the speed indicated by the speedo.”
