The PT-15 is the most sought after and versatile Pocket Tones yet. It can be used for virtually any instrument, and has specialized uses as well. A cappella and choral singers find the chromatic C indispensable, it is a must, especially when there is no piano or other reference instrument near by. It is non-disruptive when tuning during performances because the volume control dials down to a 'whisper', and a 40-voice choir can hear it at max volume.? The individual note select gets you an immediate tone, and besides all of that, the PT-15 fits right in the palm of your hand! Pocket Tones are sanitary, accurate, and a fantastic way to develop perfect pitch.