Does that include the accuracy the US Military allows you?

Recently I was riding along in a friend's car with a GPS, following along on the cartoon map. At one point the GPS said we were approaching a certain overpass that we passed a ¼ mile ago! If it's positional error can be that great, how can it's speed be spot on?

GPS Position is randomly degraded - but I have also found that speed is typically right on the money.

My Carrera is optimistic - 5-9mph in the lower speeds - closer to 10-11 over 120.

Won, If you go back and re-read what I wrote you'll see that I was testing the GPS for speed accuracy, not the odometer. The time needed to travel 1 mile at 60 MPH is exactly 1 minute. That was how I figured that my GPS was giving an accurate MPH reading.

New military technology or old? :)

Different numbers are thrown around but I think 6'-20' is a good ballpark.

Remember older technology is not as accurate. One must also take into account processor lag (in some cases) and accuracy of mapping. I have found some mistakes in Garmin's info, which I believe is supplied buy Navtech.