The Applause interactive music app listens to the note you play on your violin and then shows you if you are high, low or correct. The height of the error display is proportional to the error and disappears when the note you play is just right.
Details of every note you play are stored and can then be recalled and displayed in a variety of ways, later, this not only lets you, your parents and your violin teacher see the progress you are making, but also helps identify the best exercises for you to play next.