It would be nice if we could add a fuel up by entering the total amount in $ and the price in $/liter. These are the 2 numbers I remember when entering the data. I always need to look on the receipt for the amount of liters which is not always accurate (total price is fine but they used the regular gas instead of diesel price and so the total liters is off). Sometimes the receipt is not at hand when I am to enter the fuel up.
I find it easier to enter 60$ at 1.109$/liter rather than 54.103 liters at 1.109$/liter. The 3 fields are already in the app, the user should be able to enter 2 of the fields and the 3rd one is calculated.
Check you settings, you have the option to add in gallons (us) or litres. I put in the amount of litres, and the cost per litre and fuelly gives me the MPG and also works out the total fuel up cost too. Is this what you're after?