Definition
An instrument display method in which the value shown on the gauge is not the quantity actually being measured, but is derived from a related physical input. In the airspeed indicator, the instrument senses the difference between pitot (ram) pressure and static pressure, and the dial is calibrated to display that pressure difference as a speed in knots or miles per hour.
Plain English
The instrument doesn't measure speed directly. It measures air pressure and shows you what speed that pressure represents.
Context Anchor
Seen in airspeed indicator discussions, especially when learning how pitot and static pressure create the airspeed indication.
Derivation
‘Indirect’ comes from Latin indirectus, meaning ‘not straight’ or ‘not direct.’ Here it signals that the path from the thing being measured to the number on the dial is not straight — there's a translation step in between.
Why Pilots Care
Because the airspeed indicator reads pressure and not actual speed, its accuracy depends on conditions like air density, altitude, and temperature. Understanding that the reading is indirect explains why indicated airspeed must often be corrected to get true airspeed.
Grounding Statement
An indirect reading is one step removed: the instrument senses something else first, then displays the value the pilot wants.
Intuition Check
Do not read “indirect” as vague or unreliable by itself. Here it means the instrument gets the displayed airspeed through another measurement, rather than measuring airspeed directly.
Example Sentence 1
The airspeed indicator is an indirect reading instrument because it senses pressure differences and displays them as airspeed.
Example Sentence 2
A pilot uses an indirect reading on the ASI and then applies corrections to find true airspeed.