In my local store there is an interesting drink advertisement; a machine with two circular discs, one at the bottom and one at the top, seems to make a can of drink levitate and rotate so that customers can see the whole label. I think the machine uses electromagnets to do this, but I am still curious about it because the can never moves vertically - only slightly horizontally, and forwards and backwards. I tried removing the can once and the can didn't float when I replaced it. How does this work and how does the machine achieve such a precise region of movement for the can?