The System Impedance Curve is representative of the system impedance property inherent to an individual electronics enclosure and is generated by testing the enclosure pressure at various airflow rates. Obstructions in the airflow path can cause static pressure within the enclosure. The Characteristic Curve describes how air will flow given an enclosure’s particular obstacles and internal resistance. To achieve maximum airflow, obstructions should be minimized. However, certain obstructions may be necessary to direct the airflow over the components that need cooling. The above figure shows the nonlinear relationship between airflow and static pressure for a typical fan.