A 36% difference.
For the Variable Air Volume (VAV) system to breathe, his supply fan had to push hard enough to overcome every single obstacle in the air’s path: the louver, the filter, the cooling coil, the silencer, the duct elbows, the runouts, and finally, the VAV box itself. Too little pressure, and the top floors would suffocate. Too much, and the ducts would howl like a hurricane, wasting energy and money.