You can go to the expense of having the speedo calibrated, but I use the automated Speed Sign you come across periodically, that track your speed as you approach and it displays in BIG Digit display how fast you are going, and just glance down at your speedometer to check accuracy. Found my aftermarket one works right on, at 45, 65 and 85 ---eh---on occasion and free is always good. :bigsmiley8: