How do airspeed indicators determine the velocity of an aircraft?

Airspeed indicators function by comparing static pressure and total pressure, making use of the principles of fluid dynamics. The total pressure is derived from the ram pressure created by the aircraft's forward movement and is measured through a pitot tube. Meanwhile, static pressure is measured from a static port located on the aircraft.

When an aircraft moves through the air, the difference between the total pressure and the static pressure indicates the dynamic pressure, which is directly related to the aircraft's airspeed. This difference allows the airspeed indicator to provide an accurate measurement of the aircraft's velocity relative to the surrounding air.

In contrast, simply measuring total pressure alone would not provide a complete picture of airspeed since it does not account for the static pressure of the surrounding atmosphere. Calculating the difference with altitude does not provide direct information about airspeed but rather relates to performance and aerodynamic considerations. Lastly, utilizing magnetic heading references pertains to navigation and orientation, which are unrelated to the measurement of speed through the air.