Guitar Tuner is a tool for tuning classical and acoustic guitars. Some of the features are * It can listen to instrument sound and measure the sound frequency. * It can also produce reference sounds when touching the strings on screen. * you can tune easily by following directions like tighten-loosen * you can tune by both selecting a string or in auto-selection mode * there are also "string may be broken" warnings (in manual mode) * supports more than 50 tuning styles * callibration between 424-456Hz * metronome with beat groupings, vibration, torch, etc