This slide explains how to use a fan PQ curve against a chassis system impedance curve. Superimposing the system impedance curve and the fan PQ curve onto the same plot, they intersect at what is called the “operating point”. While a system impedance curve is constant if the chassis design does not change, choosing different fans with different PQ curves will result in different operating points for the chassis. It is with the operating point that the designer can most accurately tell what airflow the fan can supply to the chassis for a corresponding amount of pressure.