Can't figure out how to get my digital manometers to read the pressure difference between the air near the floor vs. at the 8' high ceiling. It reads 0 IWC no matter how I do it. One of my instruments is a micromanometer (reads as low as .001 IWC pressure differential), and it reads 0 IWC there too. I'm zeroing the meter at floor level, and have no hose on the "reference" port. And I gave a 9 foot manometer hose on the "signal" port with the meter at floor level and the open end of the hose a few feet from the ceiling. I'm thinking that there be about a 0.108 IWC PD there with that 8' difference in height. Why am I getting 0? It isn't an air tight room, and no fans are on.