What is a Magnetic Compass, its principle, types and errors?

5. Oscillation Error

This error is caused by turbulence or rough control movements and results in erratic movement of the compass card.
Oscillation is a combination of all of the other errors, and it results in the compass card swinging back and forth around the heading being flown. When setting the gyroscopic heading indicator to agree with the magnetic compass, use the average indication between the swings.

6. Magnetic dip Error

Magnetic dip is the tendency of the compass needles to point down as well as to the magnetic pole. Dip is greatest near the poles and least near the Magnetic Equator. The compass card is designed to operate in the horizontal, therefore, any movement from the horizontal plane introduces dip error.
The needle of your magnetic compass will be parallel with Earth’s surface at the Magnetic Equator, but will point increasing downward as it is moved closer to the Magnetic Pole.
Northerly turning error is due to the mounting of the compass. Since the card is balanced in fluid, when the aircraft turns, the card is also banked as a result of centrifugal force. While the card is banked, the vertical component of the Earth’s magnetic field causes the north-seeking ends of the compass to dip to the low side of the turn. When making a turn from a northerly heading, the compass briefly gives an indication of a turn in the opposite direction. When making a turn from the south, it gives an indication of a turn in the correct direction but at a faster rate.

Acceleration error is also due to the dip of the Earth’s magnetic field. Because of the way the compass card is mounted, the aft end of the compass card is tilted upward when accelerating, and downward when decelerating during airspeed changes. This error is most pronounced on an east / west heading. When accelerating on an east or west heading, the error indicates a turn to the north. When decelerating on an east or west heading the error is toward the south.