Heaven above

I have a Road Angel speed camera detector, which displays my speed. On my Honda CRV it always read 3 mph higher than the car Speedometer. I have changed now to a Civic Type S and the Road Angel reads 5 mph lower than the digital display Speedometer. Which of the systems is likely to be closest to my actual speed?

Asked on 3 July 2010 by JP, Reading

Answered by Honest John
On a flat straight road in clear conditions where the system can hook up to the satellites, GPS will be more accurate. On twisty, hilly roads it won't be because it measures your speed as a crow flies, across the surface of the planet. Also, anywhere it can’t pick up the satellites due to tall buildings, for example, or in a tunnel, it will compute your speed and could make a significant error. (Thanks to Peter Rodger, Chief Examiner of the IAM, for this informatioin.)
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