By adjusting the air nozzle and the auxiliary "220V AC Cooling Fan", to control air flow, air flow and pressure difference recorded corresponding value, in addition to recording the final maximum air flow and maximum static pressure, in general, but also to draw the pressure - flow chart, the full performance of a fan performance under various pressure difference. the figure that a typical fan characteristic curve. The solid line for "220V AC Cooling Fan" characteristic curve, to be measured by the wind tunnel. Dashed line is the system impedance curve, again measured by the wind tunnel. FPC and SRC junction point is the system with the use of the fan operating point OP, Qb and Pb are divided Pan is achievable using the air flow and the pressure difference. In air-cooled radiator applications, require air flow better, Qb natural to focus on the choice of reference index fan. Visible, only the maximum air flow and maximum static pressure not to choose the most appropriate when selecting "220V AC Cooling Fan". However, considering the average user can not get more exact fan and heat sink impedance characteristic curve, so a rough Fu-off is a last resort.