So I know these things aren't extremely accurate and the best way is to calculate it. I also know that some chips can alter the reading to read better. Mine wasn't working when I bought the truck, so I found the thread on how to solder some stuff on the circuit board and it fixed it. What I'm wondering is can doing this make it read even more incorrectly? I am also wondering how off can you expect these things to be? The reason I ask is because like I said mine is working now, I have run it around town only no highway and it is reading 17.1, which seems high, haven't calculated anything yet. It is also hard for me to calculate it correctly since I have 35's and the spedo is uncorrected. So I know from experience with a friends 99 that with the spedo uncorrected the readout will also read low, his was reading around 12 avg and after being corrected reads around 15avg. So I keep thinking WOW if mine is reading 17 city uncorrected that is awesome. So I guess I'm just wondering how far off can I expect this to be and possibly what those of you with the readouts are seeing on your trucks.