Well my odumator? does not work at all. I have to go to road maps to get my mileage. I only try when I'm making a long trip, longer trips lessen the error. and I'm sure that on flat ground I get 18 on a good day, and into the wind with some hills I'll get 16. towing I'll get 15-16ish. 33's with 4:88s. and I don't think that's to bad for a 83 22R.