Boss Pocket Dictionary Vol 3-5, 1986-1988:

The TU-100 fully-automatic Chromatic Tuner incorporates a built-in computer and features a 7-octave tuning range. This means you can tune just about any instrument with it. The TU-100’s 3 tuning modes include such features as: a note being chromatically selectable over 4 octaves, a very sensitive sweep meter and tuning guide LEDs.

TU-100 Chromatic Tuner

The TU-100 has other advanced features including a transpose function for trans­posed instruments, octave indication, 3-level volume selector, and even more. The TU-100’s “100” stands for 100% fully tuned” and “100% suitable for any instrument.”

  • 3 different tuning modes—Tune & Sound Manual Mode, Tune & Sound Auto Mode, and Sound Mode. In the Tune & Sound Auto Mode, you just have to play your instrument The TU-100 will automatically detect the note and the pitch of the sound. Just by observing the sweep meter and tuning guide LEDs, you can tune up perfectly. Ideal for quick, accurate tuning and also for practicing scales.
  • In the Sound Mode, you can tune while listening to a standard note through the TU-100’s built-in speaker, just as you would when using a tuning fork or pitch pipe.
  • In the Tune & Sound Auto and Manual modes, you can listen to the standard note through headphones.