Hi Seth, a water manometer was what I was going to use till I remembered the gauge I had in storage left over from my days of repairing and calibrating. Your results reasonably accord with mine, lots more work in future. I do not think many people would have a $4000 gauge lying around the house.
Mark, the idea is not mine, just trying to reproduce what I read somewhere that Arnold Jacobs said "That the blowing pressure doubles for each octave".
My next investigation will be with a sound level meter to get an idea of pressure verses loudness. Peter Kartu of the Tres Mambo Music school has postulated "That if one can blow 6 discreet levels of sound then one can play 6 harmonics, 8 sound levels, 8 harmonics etc". He bases this on the work of Fletcher and Tarnofsky Physics dept University of New South Wales. I wont get to this until towards the end of next month.