Speedo Error Myth

[proud dad]

Can't wait til my speedohealer gets here,my speedo is 10-11% off at 60 with a fresh tire [M3] 17/42 gearing

 

[race24x]

OK to this argument I would like to point out most GPS units are accurate to within a certain amount of feet I know mine tells me how many feet depending on how many sat's its picking up so with that in mind if you are accurate to within 20 feet plus of minus and you run for a quarter mile or half mile even you are trying to tell me that 40 feet doesnt make a difference in speed recording

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? Radar is not accurate opver 100 MPH or so either the only true way is a measured distance.