Any advice?

[Cajun]

Originally Posted by th3godf4th3r

but i will not be able to have a police radar me or anything

Most local police will help you with this sort of thing if you just pull over and talk to them.

You could have someone pace you in a vehicle that you think is accurate. You can also time yourself between mile makers, if you're doing 60mph, it should take you exactly one minute between markers, then use Jack's formulas to calculate which way to tweak the computer. Neither is nearly as accurate as Jack's method, but they should get you close till you can take the road trip to really test it.