Magnetic boards and components

A display device comprising a display board having an outwardly facing surface, said being of a ferro-magnetic material and having non-permanent magnetic properties, at least one substrate strip, said substrate strip having permanent magnetic properties comprising at least one pair of parallel spaced apart north and south magnetic poles extending in one direction thereof, and at least one display unit having permanent magnetic properties comprising at least one pair of spaced apart north and south magnetic poles, said poles of said display unit being spaced apart by a distance equal to a multiple of the spacing of said north and south magnetic poles of the magnetic substrate strip, said substrate strip comprising a strip of magnetic material having a pair of opposed major faces, one of said major faces having relatively strong magnetic properties comprising at least a pair of parallel spaced apart north and south magnetic poles, the other of said major faces having relatively weak magnetic properties comprising at least a pair of parallel spaced apart north and south magnetic poles, said strong north magnetic pole on the one major face being located substantially opposed to the relatively weak south magnetic pole on the other major face, said relatively strong south magnetic pole on the one major face being substantially opposed to the relatively weak north magnetic pole on the other major face.