Definition
In the context of magnetic compass northerly turning error, the pivotal point is the heading on which the compass card momentarily aligns correctly during a turn through north or south, before resuming its lag or lead behavior. More broadly in compass theory, it refers to the specific heading at which compass indication and actual magnetic heading coincide during a turning maneuver, used as a reference for timed turns using the compass.
Plain English
The heading at which the compass briefly reads correctly during a turn, even though it is wrong before and after that point.
Context Anchor
Seen in explanations of magnetic compass errors, especially why the compass behaves oddly during turns from north or south headings.
Derivation
From Latin 'pivot,' meaning a fixed point on which something turns. In aviation use, it marks the heading the turn 'pivots around' for compass-reading purposes.
Why Pilots Care
Recognizing this point shows why the compass lags or leads during turns from a northerly heading and how to compensate with timed turns or other references.
Analogy
Think of a playground seesaw resting on its center support. The board moves around that support point. The compass card has its own small support point too, so it can move differently from the airplane around it.
Intuition Check
Do not read pivotal point as “the most important point” in a discussion. Here it means the actual point inside the compass that the compass card moves around.
Example Sentence 1
Turning from east to north, the pilot anticipated the compass lag and used the pivotal point to time the rollout.
Example Sentence 2
The pilot understands that the pivotal point causes the card to swing farther than the airplane actually turns when near a northerly heading.