Plain English Meaning

The compass card is hung from a pivot so it dangles down and can swing, much like a pendulum. This lets it stay roughly level and point at magnetic north, but it also means the card tips around when the airplane speeds up or slows down.

Full Definition

A method of suspending the magnetic compass card so that it hangs below its pivot point, allowing it to swing freely under the influence of gravity and align with the Earth's magnetic field. Because the card hangs like a pendulum, it tips when the aircraft accelerates or decelerates, which is the source of the compass acceleration error.

Context Anchor

Seen in error discussions, especially when explaining acceleration error on east or west .