This app estimates your live fuel economy as you drive. The app uses the GPS to calculate real time speed and acceleration of the vehicle and then estimates the fuel economy in mpg or lphkm. Users can save their trips and review their fuel economy on a map. We recommend that you keep your phone plugged in to a charger when using Open Road. Measuring fuel economy requires constant use of the GPS, which can dramatically reduce battery life. Reviewing stored trips will not drain the battery.