Guide Tones I

The Guide Tones I voicing of Bbdim7 stacks Db and Abb from the bottom up: the minor 3rd and diminished 7th of the chord. It leaves out the root, Bb, for the left hand or the bass player to take.

It's one of the Guide Tones voicings: just the 3rd and 7th, the notes that define each chord, played over the root. The other for Bbdim7 is Guide Tones II.