The app is smart and it will remember your tank capacity and target ethanol mix values so next time you want to see how much E85 you need to add to get your target ethanol mix, you will only have to specify your current tank percentage. This way it is the fastest method to calculate how much gas and e85 you need to put in the tank. It is such a fast method, by the time you get out of your car, you already know how much fuel you need to add in the tank. Literally 3 seconds. The app is completely