I was wondering if anyone else has noticed an error in what your speedometer shows your speed to be vs. your actual speed. I have a 5 MPH differance! My GPS shows actual speed. When my speedometer shows 75 the GPS shows 70. I double checked this by haveing a friend follow me. Again, myspeedo showed 75 the GPS 70 and my friends speedo in his car 71. Is this a common thing?