I messed around yesterday with setting up an extra U-Manometer. I spliced it into the chamber after the orifice so I could measure the total pressure.If I understand it right then (Total P" - Test P" = Delta P"). Since it took most of the day to make the Manometer look like I didn't just slap it together in 5 minutes,I ran out of time to do any real testing.
But ,the little bit I did showed me right off that in the lower ranges,my inclined manometer showed less than delta P measured with the new U-manometer,and the higher ranges the inclined showed more.
At around an orifice diameter of 1,7" they're pretty much balanced out,and stayed so from 4" to 36" total P.
Will go back, do it again,and see where my Test P range is.