I want to make sure my 96 GT has an exact odemoter/speedometer reading after I install 4.10 gears. Its a T45 car w/ 245/45/17 inch tires. The speedo gear dosnt make the odemoter/speedo match up perfectly. I remember seeing a box that can be programmed by a speedo calibration shop for you gear and tire combo, but I couldnt find it. Can anyone give me some help as where to find it or how to make my odo/speedo exact.