Bike Computer "Flea"

Ok, I lost the magnet from my bike computer "flea" and have had one made up for me by the fitters at work, but the question was just asked of me, "Does the magnet need to have the positive pole out or the negative pole out ?"

I guess I could wait til I got home tonight to try both before I Loctite it in place, but does anyone here know which way ?

Cheers, Toddy