“1.2 volt per octave” aka 1.2 V/Oct is a variation of the volt-per-octave control voltage (CV) scaling standard, where a change of 1.2 volts in the control voltage corresponds to a change of one octave in the pitch of the controlled oscillator or filter. This is a less common scaling standard compared to the more widely used 1 V/Oct system.
1.2V/oct is the Buchla standard.
Looking directly at their documentation:
At the Buchla standard of 1.2v/per octave, that means that the pitch C will be 0v,1.2v, 2.4v, 4.8v or 6.0v depending on the octave being played. (Notice how conveniently that relates the MIDI “C” notes 0, 12, 24, 48 and 60.) Every ½ step higher will be .1v higher.
You can clearly see the logic behind Don Buchla’s madness.