Eliminate speedometer error caused by rear end gear and tire/wheel changes and guarantee speedometer/odometer accuracy with the GranSpeedo� speedometer calibration software from GMS. Utilizing your PC compatible laptop or desktop computer and the supplied easy to use DOS/Windows compatible software, you can recalibrate your speedometer/odometer in minutes to within 1/6,000 of 1 mph. Installation occurs in about 15 minutes. Each system includes instructions and everything you need to calibrate your speedometer except the computer.