Usually, due to the relatively low value of the static pressure of a fan, the unit that this pressure is expressed is milibar, mm H2O, psi, mm Hg, kPa, hPa. In the US, inches H2O.
Pressure is shown with white curvy lines. The closer the lines are to each other in a certain area, the higher the pressure is. The farter apart they are, the lower the pressure is in that area.
atmospheric pressure in measured in millibars