A Fender AX-12 Chromatic Auto Tuner is a compact electronic device used to accurately tune musical instruments—especially guitars and basses—by detecting the pitch of each string and indicating whether it’s sharp, flat, or in tune. Being chromatic, it can recognize all 12 notes of the musical scale, making it suitable for standard and alternate tunings as well as other instruments. The auto function means it senses the note you play and displays the tuning result automatically, helping musicians tune quickly and precisely before practice, recording, or live performances.