Abstract
In 1966, Ervin M. Wilson invented his first combination product set – a rational, non-centric structure that
musicians can use as a scale. In 2005, David C. Keenan invented a guitar fretboard that can play all twenty notes
from a particular combination product set. I propose a Halberstadt keyboard design that makes use of a seventynote
combination product set. The combination product sets used by the two instruments are not reduced to the
octave, and they do not repeat at the octave.
