The guitar has a useful kind of symmetry.

Standard guitar tuning, from the lowest string to the highest, is E–A–D–G–B–E. Most neighboring strings are a perfect fourth apart: five semitones. The exception is G to B, a major third of four semitones.

Each fret raises a string by one semitone. After twelve frets, the note name repeats an octave higher. Guitarbacus uses these relationships to lay the notes of a scale across all six strings.

The highest string appears at the top of the diagram, as it does in guitar tablature. The open-string column is followed by numbered frets.