Somehow a lot of our little plotting compasses were pointing to S when presented with the North end of a magnet ie pointing 180 degrees in the wrong direction. Don't know if any of you have experienced this but my tenacious colleague Katrina, undeterred by my response of "buy some new ones" and CLEAPSS advice of "take them apart and use a bar magnet to stroke the needle to re-align the domains" (very fiddly), has discovered that if you hold the North end of 2 magnets either side of the compass so that they repulse each other and hold them there for 30 seconds then take them away, the needle will once again point to North. 
