This video explains the deviation of the ship's magnetic compass.
The terms of deviation, variation, compass error are explained.
The difference between true, magnetic, and compass North are also explained.
The process of "Swinging a compass" towards making a deviation card is also explained through animations.
Legal requirements concerning the magnetic compass and its adjustments are also explained.
Previous video explained:
Magnetism - an introduction to the ship's magnetic compass: https://www.youtube.com/watch?v=X0caJUWPVrA&t=3s
The parts of the magnetic compass:
https://www.youtube.com/watch?v=xqHIPllV3Ow&t=12s
Ship's magnetism and how it is acquired: https://youtu.be/RffiU4Q7vXE
How does the earth's magnetism influence the ship's magnetism:
https://www.youtube.com/watch?v=8VIqsIEwbRI&t=29s