Use the internal microphone to tune acoustic guitars. Pluck a string and the tuner will automatically switch to the nearest note, indicating sharpness with LEDs to the right of center and flatness with LEDs to the left. Turn the mechanical tuning peg on your guitar to bring the lit LED to the center. Repeat for the remainder of the strings on the guitar.
Connect an electric guitar or bass using a 1/4-inch phone plug guitar cable to the input on the GT-3, which is indicated by a left-pointing arrow on the tuner. Tune your instrument the same way as described for acoustic guitars.
Connect the output of the GT-3 to the input of an effects pedal or pedal board. The output is indicated by a right-pointing arrow, and uses a 1/4-inch phone plug connection as well. This keeps the tuner in the guitar signal path for performance use.