Very nice

I used a pocket watch style device with rotating, concentric rings in a bit of flash fiction, once. I also wrote a transmuting cane/sword thingy controlled by a rotating cylinder just below the handle/hilt, but I like the sheath idea better.
Oh, and on a slightly different note, I once ran a pirate alchemist who kept water-based equations on wooden planks tied to the side of her ship. When she wanted to use one, se just tossed it overboard. To turn it off, she just pulled it up out of the sea.
--Dan