6(Book). The Guitar and Music Theory Wheel is a visual two-sided music theory reference tool for guitar and piano, covering every musical key. It contains a book's worth of music theory while still fitting in your guitar case The curved guitar neck design allows for easy visualization of theory on the guitar. The Guitar Wheel is an all-in-one tool for chords: major, minor, diminished; chord inversions; and scales: major, minor, diminished, pentatonic, and blues.