A couple suggestions.
 

Given the thread it's in, I thought it might get lost and IMHO it's too good an idea for that to happen.In the fuel logs it would be great if we could tag fills as reference or non-reference. (If you don't like the term reference, pick a different one like: average, ordinary, typical or representative.)

About 1/2 my daily 150 - 165 mile newspaper hauls are normal/average/representative. The others entail conditions (extremely late print runs, bad weather/road conditions, broken paper racks ...) that significantly skew FE data. I imagine that most people mentally categorize as typical/non-typical. If we could tag and then filter on the tags, patterns should be more apparent.

With all of the explaining and DIY-ing on this forum, a "Thanky" button is a must. I'm surprised this didn't come up earlier.
The idea with labelling "typical" tanks isn't bad, but I understand that the average will be calculated from all tanks, not only the "regular" ones?

I wasn't thinking of calculating average MPG based on "typical" tanks, but your comment has got me to thinking. We can already label tanks anyway we want in the Details section of fuel log entries. What's really wanted, is a way to view one or two selected subsets of a fuel log entries on an ad hoc basis. As a concrete example. Look at my fuel log entries for DaBlueOne. On 2009-04-07 and 2009-04-08 weather conditions were sufficiently similar and my load of newspapers arrived sufficiently on time to make those two fills useful as reference points. If I'm lucky, there will soon be enough similar matching circumstances to make a valid comparison between accelerating from 32-50 mph in 5th gear vs accelerating from 32-40 mph in 4th and from 40-50 mph in 5th. If I'm not so lucky, temperatures will gradually creep up and I'll have to establish a new base line.

About the missing base line data: Although I don't have base line data in the EcoModder fuel log, that doesn't mean I haven't kept track (~47.5 mpg at 15*F and light winds), only that the EcoModder fuel logs are much less convenient than my stack of gas receipts (printed with date, gallons and $/gallon) the select few of which are marked Tues REF RUN, Wed REF Run ... (Miles travel per fill is implied by the day of the week and REF. Light winds < 15 mph are implied by REF. Temperature implied by REF varies with the time of year. Current range of temperature implied by REF is 10*F - 30*F.)