The world's top-selling stage tuner, the BOSS TU-2, evolves and improves with the debut of the TU-3. Housed in a tank-tough BOSS stompbox body, the TU-3 features a smooth 21-segment LED meter with a High-Brightness mode that cuts through the harshest outdoor glare. Choose between Chromatic or Guitar/Bass tuning modes, and enjoy visual pinpoint tuning verification with the Accu-Pitch Sign function. The TU-3 incorporates a convenient Note Name Indicator that can display notes of 7-string guitars and 6-string basses, while the Flat-Tuning mode can support up to six half-steps. It's the standard tuner that no guitarist or bass player should be without.
Features 
- 21-segment LED meter with brightness control
- High-Brightness mode enhances meter visibility outdoors
- Accu-Pitch Sign function provides visual verification when tuning is complete
- Chromatic and Guitar/Bass mode (tune by string number, with support for 7-string guitars and 6-string basses)
- Flat tuning is supported with Guitar Flat mode, which allows for "drop" tunings up to six semitones below standard pitch
- Signal is automatically muted when the tuner is on
- Tuning Range: C0 (16.35Hz)-C8 (4186Hz)
- Reference Pitch: A4=436-445 Hz (1Hz step)
- Tuning Accuracy: +/-1 cent
- Power Supply: DC 9 V: Dry battery 6F22 (9 V) type (carbon), Dry battery 6LR61 (9 V) type (alkaline), AC Adaptor (PSA series: optional)
- Current Draw: 30 mA (DC 9 V), 85 mA (DC 9 V, when High Brightness mode is on)
- Accessories Included: Owner's Manual, Leaflet ("USING THE UNIT SAFELY," "IMPORTANT NOTES," and "Information")
Uses 9-volt battery or PSA-120 adapter (not included).