C Diminished Seventh chord (Cdim7) on the guitar fretboard

The C Diminished Seventh chord (Cdim7) is made of C (the root), Eb (minor third), Gb (diminished fifth) and Bbb (diminished seventh). 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 diminished seventh stacks three minor thirds, so its four notes divide the octave into equal parts. That symmetry means the same shape can be named from four different roots, and it repeats at regular steps along the neck. It is the fully symmetrical sibling of the half diminished chord.