Since i bought my 15 scat pack there has always been difference a between the speedometer gauge and the digital speedo on the evic, today i went in through HPT scanner and found the tire size was incorrect ( smaller than whats on the car) i fixed that with diameter from MFG specs and the difference between evic and gauge increased! gauge stayed the same (80 mph at 1800 in 6th gear), evic dropped from 78 to 75 mph does anyone know how the speedo system works and if the gauge or the evic is the accurate one?