Professional chromatic tuner for Piano, Guitar, Violin. (E Tuner is tuned relative to A446 Hz) Features: - High Accuracy ±2 cent (±0.02 semitone) - Tone generator (20 - 20 000 Hz) - Frequency meter Tune your acoustic guitar with E Tuner free. App uses device microphone for precise tuning your musical instruments. Also app can use to Headphones test for engineer and professional sound designer. This helps choice headphones which one offers best performance.