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. Additional Information: You have the option to select what your current ethanol content is if you measured it with an ethanol content analyzer and the app easily calculates how much E85 and how much gas you need to add to reach your target ethanol mix. You can also specify the ethanol content of your E85 if you measured it with an Ethanol Content Analyzer, so this way you get an exact guide as to how much E85 and how much gas you have to put in the tank. Tank Capacity -Specify the capacity of your tank Tank Percentage -How full is your tank E85 Ethanol Content -What is the Ethanol content of your E85 what you are about to put in the tank Target Ethanol Mix -What your desired ethanol mix is, for example (E30 E40 E50 E60 E85) Current Ethanol Mix -What your current ethanol percentage is of your current fuel in the tank For any questions please feel free to contact at [email protected]