A customer asked me to make him an interval scaler for a PAiA. PAiA is a V/Hz so you can't just add or subtract voltages from the CV. You can, however, multiply them with scale factors. -1 octave or +1 octave are simply multiplying by 0.5 or 2. He wanted a major and minor third and a major fifth. Those you can create by multiplying by 1.1892 for a minor third, 1.2600 for a major third, and 1.4884 for a major 5th.
I made it in a 2-wide panel with one CV input and four separate scalers, each with 6 settings and 2 CV outputs. It came out very nice. I have a demonstration video with four 4720 oscillators on my
PAiA Hz Interval Scaler page.
Dave