Help!
 

Can anyone explain to me how to use this site to get accurate figures??

If i do the calculation on a brim to brim fill I get aprox 28MPG as my figure this site is telling me I am doing 34mpg.

It seems to be putting in an incorrect value for the fuel quantity, I must be doing something wrong HELP!!

Looks like you have your cars set to track with gallons instead of litres. Here's more info about choosing units when you create a vehicle: How do I add fuel-up data in Litres and Kilometers?