Every model page on this site shows the measured P-Q curve; here is how to use it.
Axes
Horizontal: airflow (m³/h). Vertical: static pressure (Pa). Each curve is one speed grade or control voltage, measured at standard air (20 °C, 101.3 kPa, 1.2 kg/m³). At altitude or high temperature, air density drops and so does the pressure the fan develops.
The operating point
The fan runs where its curve crosses the system resistance curve — a parabola through the origin (pressure rises with the square of airflow). Enter your duty point in the curve tool on the model page: it draws the point and tells you which grade covers it and by how much.
Reading margin
Margin is the pressure the fan could still develop at your airflow beyond what the system needs. Aim for 10–25%. Below 8% the fan sits close to the limit; above 40% you are paying for pressure you do not use.
Left of the peak
Backward curved and axial fans have an unstable region left of the pressure peak (stall). Select on the right-hand, falling part of the curve; the selector only accepts points there.