On button compasses again...
Further research, and I can report that there is no evidence that residual magnetic affects effect or influence the behaviour of a compass needle in any way, provided the magnetic effect cannot influence both polls of the compass equally at the same time (thus allowing the compass to realign) and providing the needle in the compass is free to move.
So storing a compass in proxility to a magnetic source, even a large one, will only influence the behaviour of the needle after the magnetic source has been removed, if it was able to exert the same force on both polls of the needle equally and simultabiously.
The only way I have succeeded in doing this in real life is to sit one pole of a powerful magnet, directly on top of a compass and leaving it there until the polarity of the compass has been changed. It changes because only one pole is present and it pulls on both the nort and south poles of the compass at the same time, realigning the compass with prolonged exposure because the compass needle cannot align itself to the magnet field it's it, and to the poles within the steel comprising the needle align themselves to the field.
The same tests with magnets placed adjacent to a compass leave no affect in the compass whatsoever.
To answer someone elses query on another thread, you do not get button compasses balanced for different regions of the world. All compasses point north wherever you are on the planet. The 'weighting' of a compass for different region of the world is a deffinition of the physical mass of the needle at one end versus the other, and that is because in different regions of the globe (generally in and below the equator) the needle is physically pulled (tilted) down towards the planet, as magnetic north is actually down and through the planet.
A northern hemisphere compass used in Australia where the affect is most pronounced will experience problems where the north tip of the needle dips and touches the base of the compass and hamper or preven free rotation. So southern hemisphere (compasses are weighted in regions 1 through 5) compases have heavier souther neds to their needles to compensate and balance the needle.
For obvious reasons, this is an issue only in compasses with a larger needle. The longer the needle and the shallower the distance between the tip of the needle and the base, the greater the problem.
Button compasses do not exhibit this phenomenon for two reasosns. The distance between the needle and the base of the compass is quite substantial as a factor of the distance between the pivot and the needle tip, and the power of the magnet within the compass needle is incredibly small when compared to traditional lensmatic or base plate compasses.
In conclusion, there is no way the magnetic affect of the presence of a knife or other piece of camping equipment can permanently alter the polarity of your compass. It is an urban myth.
