[XB GS 351 Coupe]

I just read all that and in the end it is the driver/owner/operator of the vehicles responsibility to ensure the speedo reads correctly.

For examle I own and drive several cars, and am well aware if my speedos read accurately, I recently fitted 33" mud tires to my 4x4 daily driver (32" standard, and yes it does see a fair bit of off roading, hence why the tyre upgrade), the first thing I did was check the speedo with my GPS, as I also do a lot of highway driving, the result was that the speedo now reads spot on (it did not before and I was aware of this also).

It's your vehicle so it is your responsibility to ensure it works correctly enabling you to drive legally.

Another thing you seem to have missed/ignored/unaware of, is that police radar equipment gives you a 'discount' on your actual speed, so the reading the officer gets already takes into account the possible worst case scenario equipment error, and adjusts it in your favour. So the radar will give you a lower reading than your actual speed no matter what.

I am not sure what the actual error percentage is and it is possibly different for different devices (hand held/vehicle mounted/camera etc), but lets say if the device has a worst case possible error of 5%, and you are traveling at an actual speed of 100km/hr, the speed that gets registered is only 95km/hr (based on a hypothetical 5%, it might only be 2% or what ever)

So if you are traveling at an actual speed of the speed limit you will never be booked (obviously) and even if you are travelling slightly over the limit, generally the speed detected will be lower than the actual speed you are travelling.

So personally I think people worry too much, just returned from a 250km drive and mainly used the cruise on 100km/hr in a 100 zone (most of the drive apart from a few towns I went through), seen a few highway cars cruising and they never even glanced at me sideways.