The Hypertech Speedometer Calibrator is ideal when you don't need the programming capabilities of the Max Energy but you larger tires or a different differential and you want an accurate speedometer. The Speedometer Calibrator programmer plugs into the under dash OBDII port, select your tire size and gear ratio, and in a mere minutes the vehicle's ECU is reprogrammed for accurate speedometer and odometer readings. In addition, Hypertech's Speedometer Calibrator can also read and clear diagnostic codes (check engine light). Avoid a trip to the dealer and forget buying a separate, expensive scanner.