Hol Rock was a going to be a breakthough for music according to Holly. It involved decimalising the musical scale. Instead of the octave, it was now the decatave and there where two new notes, H and J. He added "wo" and "bo" to the solfeggio scale: "Do Re Mi Fa So La Wo Bo Ti Do."
Holly also confidently predicted that, due to this enlargement of musical scales, triangles would have four sides and pianos would be the length of a zebra crossing. However one down side was that women would have to be banned from playing the cello, unless they did it side saddle or used birthing stirrups.
- Hol Rock was mentioned in the Series II episode "Kryten".