ALWAYS trust the compass.  Often I find myself having to remind myself of this simple little mantra when in bad visibility.  It is very easy for us to walk in what we think is a straight line but is in fact a curve.  And it is also very tempting for us to walk on a compass bearing, which should be a straight line, and think to ourselves that we are walking in a curve.  This tendency also highlights the common misconception encountered when teaching navigation; that the compass is kept out, and in hand, to follow.  If you try and walk and keep the compass in hand and ‘follow the compass’ the tendency to not walk in a straight line will make you walk off the bearing.  It is better to imagine the bearing as a straight line on the ground that you are trying to keep to.  Use the compass to see the straight line on the ground and try and pick an object that is far away and on the line (like a rock or distinctive blade of grass).  Then put the compass away and walk to that point, then repeat the process again.

But should we always trust the compass?  Over the years I have have seen a strange thing happen from time to time; compass reversal.  i.e. the north on the compass suddenly starts pointing south! It is a strange thing to see but can be explained by the use of strong magnetic fields.  If a compass is brought into a magnetic field facing the wrong way it can be re-magnetised.  This needs to happen quickly so that the needle does not get a change to spin and line itself up properly.

the one on the left is ok, the one on the right has been scared reversed

It can even be a problem while out on the hill.  Strong magnets are more common than they used to be and they can often be found in glasses cases and even some hydration tubes.  A friend of mine was out at the weekend and had his compass reverse on the hill, probably due to coming too near his hydration tube magnet too quickly.  So, was it possible to continue using the compass with the needle the wrong way round?  It turns out that it is more difficult than you would expect as the compass needle sticks too much.  Compass needles are ‘balanced’ when they leave the factory.  This means that the needle has a little extra weight added to one end to keep it level.  When the compass has been reversed the needle is left dipping down too much on one end making it stick.

There is a solution to fixing a reversed compass or a lazy compass (one that is too weak to turn fast), it involves bringing the compass carefully near a very, very strong magnet.  A friend of mine calls this scaring the compass.  If the compass has been reversed then you figure out which way the compass wants to align with the strong magnet.  Then you turn the magnet 180 degrees around , holding it away from the compass.  Then you very quickly introduce the compass to the magnet before the needle has a chance to align itself the way it wants to, then leave them together for a while.  If the compass is lazy then it is a simple matter of bringing them close together slowly then leaving them for a while.  Just a matter of sneeking up on it and scaring it with a strong magnet.