The ÆP method of space static pressure control is relatively straightforward and a schematic of it is shown in Fig. 1. In this method, the differential pressure is controlled with a differential pressure sensor and a controller and the supply air volume is simply a function of the ÆP, the set point, and the PID constants a and ß. Another similar method of static pressure control utilizes the Bernoulli principle which states that a pressure gradient will accelerate a fluid to a velocity proportional to the square root of the pressure differential. These pseudo-ÆP systems utilizes an air velocity probe mounted in a tube inserted into a hole in the wall between the controlled space and the reference space. The differential pressure will induce air to flow through the tube and the velocity of the air is sensed by the velocity probe. A controller then varies the supply air volume to the laboratory to maintain a velocity pressure set point.