A cane with a magnetic guide for blind people is currently being patented by the Minnesota Mining and Manufacturing company of St Paul in Minnesota, USA. The tip of the cane houses a sensor that measures the strength of a magnetic field along a guide track. The track is made from three parallel, magnetised strips: two outer regions which are strongly magnetised and a central region which is lightly magnetised. The cane emits a tone that changes with the strength of the field, keeping its user on the right track (New Scientist , Vol 157, No 2118).