This app. calculates the optimal sail range for all your windsurf sails. As you normally use various sails over a very wide wind range, this quiver app shows you what sail sizes you need to have; Very easy to use, results are displayed immediately. Only two parameters to be set: your core sail size and sail increment. This app can be used for all types of sails: from wave sails to racing sails and anything in between. The app runs on artphones as well as tablets.