In general, "Cooling Fan Manufacturer" feature is very difficult to measure airflow, but there are still two ways method used to measure the static pressure and air volume, one for wind tunnel testing, another way to dual box. Air volume and static pressure characteristics specifications are measured using dual-box approach, in which we will explain what is meant by double-box way. "Cooling Fan Manufacturer" variable exhaust air out of the system to adjust the density of the air, opening of the nozzle will cause the instantaneous static pressure and air volume change instantaneously, and then reads each of the hydro static pressure reading on the gauge. "Cooling Fan Manufacturer" maximum air volume measurement is to adjust the variable exhaust system makes the condition of zero static pressure measured in the box B in the air volume. At this point, static pressure difference A, B box between the fan and spraying operation