Definition
A small adjustment value, listed on the magnetic compass correction card, that tells the pilot what heading to fly on the magnetic compass in order to actually track a desired magnetic heading. The values compensate for residual deviation errors caused by the aircraft's own electrical and magnetic fields after the compass has been swung and adjusted.
Plain English
A note showing how far off the compass reads on different headings, so the pilot knows what number to put under the compass to actually fly the heading they want.
Context Anchor
Encountered during cockpit checks after engine start, when the pilot verifies that the magnetic compass and its correction card are present, readable, and usable.
Derivation
Correction comes from a word meaning “to make straight” or “set right.” In this use, it does not mean repairing the compass; it means applying the printed adjustment so the compass reading points you in the intended direction.
Why Pilots Care
Provides accurate magnetic headings for navigation and prevents cumulative heading errors during instrument flight.
Analogy
It is like knowing that a bathroom scale reads two pounds high and mentally subtracting two pounds each time. The scale still works, but you need the known correction to use it properly.
Intuition Check
Do not assume “correction” means the compass has been physically fixed. Here it means a printed adjustment the pilot applies when using that specific aircraft’s compass.
Example Sentence 1
To fly a magnetic heading of 090, the compass card correction tells the pilot to actually steer 092 on the compass.
Example Sentence 2
With the compass card correction noted as plus three degrees, the actual magnetic heading was confirmed.