Pressure can be measured using an aneroid, Bourdon tube, mercury column, or various other methods.
With this simplification, Bernoulli's equation for incompressible flows can be expressed as[2][3][4] where: Every point in a steadily flowing fluid, regardless of the fluid speed at that point, has its own static pressure
The British Standards Institution, in its Standard[10] Glossary of Aeronautical Terms, gives the following definition: An aircraft's static pressure system is the key input to its altimeter and, along with the pitot pressure system, also drives the airspeed indicator.
[11] The static pressure system is open to the aircraft's exterior through a small opening called the static port, which allows sensing the ambient atmospheric pressure at the altitude at which the aircraft is flying.
In flight, the air pressure varies slightly at different positions around the aircraft's exterior, so designers must select the static ports' locations carefully.
Wherever they are located, the air pressure that the ports observe will generally be affected by the aircraft's instantaneous angle of attack.
[13][14] A designer's objective in locating the static port is to minimize the resulting position error across the aircraft's operating range of weight and airspeed.
At least one author takes a different approach in order to avoid a need for the expression freestream static pressure.