Is the speed off?
My unit uses the SiRFstarIII chipset, 20 channel. At the time the speeds were recorded I had 10 satellites locked and clear view of sky.
My findings are that both the portable sytems READ 2 to 3 M.P.H.
LESS than the actual speedometer in my E class across the all the range (10 to 120 M.P.H).
e.g. Speed reading on cars own speedometer 30 M.P.H .....GPS reads (27/28).
You will find most moden cars speedomerters are set MINUS - a little because in my opinion it gives more tolerance to law inforcements on speed cameras,radar, etc.
Les............Chesterfield U.K.

My findings are that both the portable sytems READ 2 to 3 M.P.H.
LESS than the actual speedometer in my E class across the all the range (10 to 120 M.P.H).
e.g. Speed reading on cars own speedometer 30 M.P.H .....GPS reads (27/28).
You will find most moden cars speedomerters are set MINUS - a little because in my opinion it gives more tolerance to law inforcements on speed cameras,radar, etc.
Les............Chesterfield U.K.
If you get close to 0.5 mph errors, you probably have tyres close to the max allowed tolerance in their size, or perhaps you actually have a higher than rated tyre diameter.


