Incorrect mpg

[RussTaylor]

I'm sure you're right, and I'm missing some subtlety, but can you explain where this doesn't work...

I have filled my car up, it took 50ltrs (doesn't matter). On my odo I have 100 miles. So starting point = full tank and 100 miles on odo.

I drive around, and do a partial fill up, so 10 litres, my odo reads 110 miles.

I do the same again, this time I fill up 20 litres, and my odo reads 140 miles.

I then drive around, and perform a full fill up which takes me 30 litres, and on my odo I have 200 miles.

Since the last full tank (our reference, no different than my very first fuel up on Fuelly) I have travelled 100 miles, and used 10 litres + 20 litres + 30 litres.

This is the amount of fuel I have put into the tank to return to our reference point (full tank). So 100 miles and 60 litres...

Sorry to keep bashing the point but I disagree with both of you. You say you have no point of reference, but you do from your last full fill up. You have how much you put in the tank in between, and how much it took to fill it up again.