http://itunes.apple.com/us/app/gas-by-numbers/id531541048?mt=8 I made Gas By Numbers as an easy to use Gas consumption and Gas efficiency calculator. Enter the travelled distance, enter the amount of gas you refilled and optionally, enter the price per Liter/Gallon of gas. You get the results right at the pump. You can save the data for later review on your iPhone or iPod or you can export your data to your Mac or PC. You can even enter older data by using the same steps as described above but by entering a date from the past (maybe from an old receipt) once you get to the point where you save your data and get prompted whether you want to save the data for the current day or for a different date.