speeding and speed

[olfella]

I have a GPS hardfixed in my BA and therefore hardly ever lookat the speedo because I know it reads low. When passing speed traps etc I always use the GPS and have never been pulled over. What I am getting at is I am told the speed readout on the GPS was most accurate and therefore I take it as gospel.

Now on a recent trip in Vic, I went under one of those check your speed thingos and I was doing spot on 110 on the GPS. The speed thingo said I was only doing 107!! meanwhile my speedo is reading up in the 120 mark.

My point in raising this is what sort of defence does anyone have when pulled over to be told they were 2-4 k over the limit. What makes the coppers equipment so accurate and why the hell cant they put that in everyones car so we all know how fast we really are going?