This app uses very simple trigonometry (well, really just similar triangles. ) to determine how far you are from the green. It does not use GPS, so you don't need to connected to internet to use it. I developed this application to use with my dad when we would go golfing. I could not find any free apps that could determine our next shot's distance, and all the paid apps used GPS. This has many drawbacks: first; if your course is not pre-loaded into the GPS, the app becomes useless, second; if you do not want to waste data and money, you have no choice, third; because golf courses always change the location of the pin on the green, the GPS usually just tells you the distance to the center of the green, not to the pin, fourth; GPS's have an uncertainty range. Well all that has changed with this new application that can be operated in Airplane Mode. Just hold the phone/tablet out in front of you while facing the green and line the two horizontal bars onscreen with the top and bottom of the actual flag post. Play around with how far you hold the phone away from your face to see what works best for you.