[tfarhood]

The Autometer speedo is a mechanical speedo. (as opposed to electronic). There is no calibration for it other than choosing the most appropriate gear that connects to the transmission tailshaft gear. Based on rear end gearing and tire size you can calculate which color gear (they are color coded) will work best for you. As for checking the accuracy, a small hand held GPS is the easiest and most accurate way to verify it. If you don't have one, I guarantee someone you know has one. I checked my BDR with GPS and it was about 3-4 mph slow at 25 mph, 2-3 mph slow at 60 mph, and dead on at 110 mph! The interesting thing is to check all of your autos with GPS, you'll be surprised at how far off some factory cars are.