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I might be wrong but I'm not sure it does. I think you just hold the knife against the angled block don't you? I'm also interested in hearing how well it actually works. My partner has shown me a few videos of it seemingly getting very good results but it's hard to tell how much of it is marketing bollocks. It seems like a good idea for the casual knife sharpener (myself included) on paper though.
I like it. It looks like it relies on your knife having a magnetic blade.
One of mine does, the other, not so much.