Compass is installed on an iron ship

[indigojoker]

when a compass is installed on an iron ship, why must there be small correcting magnets installed near the compass? Is it because the iron is itself magnetized somehow?

 

[Bill Foster]

Not necessarily. But iron is a magnetic material and will affect the compass needle. Just as you can use magnets to pick up nails. The nails aren't necessarily magnetized, yet they are still attracted to a magnet.

 

[stewartcs]

It could be due to the fact that true north is different from the magnetic north.