Cowlitzfisherman hit it on the head. sounded like a ex-meat cutter,,, if you have access to high pressure sodium bulbs,, inside is a cermic element about five inches long.. great little item for straighten the edge.
bear in mind as you steel the knife its lifting the rolled edge back up. with time the edge will break off thats when the stone will come back in to play... after steeling the blade lightly drag it over your finger nail. a straight edge will drag or pull a broken or dull will glide easly.