C Sixth chord (C6) on the guitar fretboard

The C Sixth chord (C6) is made of C (the root), E (major third), G (perfect fifth) and A (major sixth). The fretboard shows every one of them across the neck in standard tuning (E A D G B E), and plays them back so you can hear the chord.

The sixth chord adds a major sixth to the major triad, giving four notes with no seventh. The same notes appear in the minor seventh chord a sixth higher, so the neck shows two names for one shape. It sits between the plain major triad and the major seventh.