Thanks for the replys - I guess that are no real clear cut answers.

I would think that if you took your total mileage over lets say 10 tanks and divided by your total gallons you should be close to your nav avg? This would let you average out the air pockets, etc in your tank fill-ups?
This would have to be the most accurate right?

On this tank I didnt reset my NAV average - yet I'm still getting 1mpg swings especially on short trips. I would think with 400miles in the computer that it would take more than a 5-10 mile trip to swing the overall average by 1mpg?

If it stores 2000min of driving/mpg info - Wouldnt keeping the data give you the best overall actual number to match your tank data? Especialy since it would be averaged over 3-4 tanks? I would think the swings would be slow - unless you totally change your driving techniques and the old data gets replaced with the new data?

Am I missing something?

I've searched for the old threads, and it doesnt seem like their is a conclusion?

Without the programer for the NAV it might be hard to figure out how often they sample the data or if they avg out your instant readings over the whole past 60seconds before showing the history data on the screen?

Thanks for answering the questions!

Gary