I was comparing my purchase records with how much Fuelly says I've purchased over the year, and I discovered that the second fillup after my partial fillup doesn't have a total purchase price calculated. Could this be fixed?
No. This is how the site works. When you do a partial fillup, Fuelly cannot calculate this. So what happens is it then goes from the next full tank (which it also gives a 0) then it can recalculate again correctly on the tank after that.
The reason this happens is it is difficult to code correctly the math for it on here from what I understand. I know my Excel sheet I use can do it, but I have to do the calculation entries eslwhere on the page, and I have to know the near exact capacity of my tank.
You could do this another way as well. Add the fuel amount from both the partial and the full tank together. Then add the purchase totals from both together. Divide the total cost by the total gallons to get your price per gallon. Then enter those details as one fuelup entry. It won't reflect the correct tank volume pontential of your particular vehicle, (it would look like you have a bigger tank for that fillup) but the mpg, usage, and costs will come out the same.