Pretty sorry state for any indicator in 2006 not to be able to give you accurate info. For a marque or dealer to say, well, it's allowed 12% (or whatever) and it's only off by 10% or less... really! This is 2006, how hard is it to have a device included as a basic instrument that measures speed and distance accurately?
A speedo should be at least able to give you info as accurate as the radar that can be used to measure you against the posted limit.
How long would you keep a watch that were 'allowed' to be up to 10%, even 2% off all the time?
And then there's that worthless tach!
