Japanese self-sharpening mechanical pencils give the lead a tiny turn every time you lift the tip

https://www.youtube.com/watch?v=H_OXoxymeho

Uni's Kuru Toga Roulettes are mechanical pencils that solve a problem I've never had, which is that the tip wears differentially, eventually creating a blunt instrument (I am a clod whose draftsmanship looks like I tried writing in a zeppelin caught in a tornado, so this is not a problem for me) -- the Roulette contains a tiny gearing mechanism that rotates the lead by a quarter-turn every time you lift the tip (e.g. between words); this creates an even wear around the lead's tip, keeping it sharp and reducing the likelihood that it will snap. (via Core 77)