system not calculating mpg if last fuel up was partial.
 

Mpg should be calculated for the two combined miles and fuel consumption for both fuellings. Why doesn't it show the average mpg when it is easily calculated

Fuelly was set up on this belief:
https://www.fuelly.com/faq/3/fill-the-tank

However, we have received quite a bit of feedback requesting the calculations be changed. We're considering it and it may roll out in a future update. No ETA at this time to report though.

That's ridiculous if I may say so! I fueled up locally (partial tank) before a long highway trip so I would not have to pay Thruway prices. Now Fuelly is useless for me... I also fueled up in Michigan before entering Canada as there are extra charges there, so it happened again. You should re-examine this issue.

Did you fill the tank up? From what I've heard, usually when gas prices are less expensive than in the area you're going, one tends to fill-up to avoid running low when in the expensive areas.
Only reason I ask, is because that would not be considered a Partial fill.