Press the red "standby/on" button to power up the tuner. The screen will show the name of the selected instrument -- guitar by default -- in the top right hand corner, and an arching line stretching across the middle and top of the display.
For instruments with pickups, connect with a guitar cable to the input jack at the lower right-hand side of the GA-40. If you wish to keep the tuner connected during live performance, use the output jack on the opposite side of the tuner to connect a guitar cable to your amplifier.
Select your desired instrument by pressing the "guitar/bass" button, located directly underneath the "standby/on" button. The name of the instrument displayed in the top right hand corner of the screen will change with each press of this button.
Play the string you wish to tune. If you are playing an acoustic guitar or bass, hold the tuner close to the sound hole of your instrument. The display needle will adjust to the frequency produced by the string, and one of the three lights on the top side of the display screen will illuminate.
Tighten the string if the flat “b” light illuminates and the needle points left of center. Loosen the string if the sharp “#” light illuminates and the needle points right of center. If the green light in the center illuminates and the needle points to the center, the string is in tune. Repeat this process for each string. For a standard six-string guitar, the notes displayed in the top left of the screen for the E, A, D, G, B and E strings are “6E,” “5A,” “4D,” “3G,” “2B” and “1E.” For a standard four-string bass, the notes displayed for the strings E, A, D and G are “4E,” “3A,” “2D” and “1G.”
Press the “flat” button, directly underneath the "guitar/bass" button, to lower the pitch of the displayed note by one semitone. A “b” symbol will be displayed on the screen to indicate that the note is one semitone flat. Repeatedly pressing the button will set the note to be tuned multiple semitones high, which is indicated by the number of “b” symbols displayed in the top left corner.
Press the “sound” button, underneath the “flat” button, if you wish to hear a guide tone for tuning the instrument. Press the “sound” button multiple times to change the note that is produced.