MPG Incorrect Calculation

[Neanderthal]

What am I doing wrong here?:

Tank #1, full from dealer, filled @ 261.9 miles (289 total miles) 8.278 gallons. No post at Fuelly.

Tank #2, 248 miles (537 total) 8.183 gallons, fuelly says 33.6 MPG, math shows 30.3.

I should have two posted tanks, 31.6 and 30.3.

What's going on?

[Draigflag]

For the 2017 Soul? I can see both tanks, if I switch to US setting, one is 31.64 MPG, and the other is 30.31 giving an average of 31 MPG.

[JockoT]

The first tank has no miles input therefore Fuelly will disregard it.
Second tank shows 30.976 litre for 275 miles. This gives a figure of 40.46 mpg UK or 33.63 mpg US.
To get Fuelly to take both fill ups into consideration you would have to create a set of figures for when the dealer topped up. Use the figure for mileage of 261.9 miles and an initial fill up. Then change the 1st August fill up to include the mileage of 550.9.
Either that or your average will be from the first time YOU topped up.