Metric Ruler for Keychains

For those nerdy times when you want to do some rough CAD on the bus without calipers...

Inspired by tecaccessories.com/Centipede, I wanted something with 1mm accuracy, cheaper than $22, and to design it myself. I'd love a real Centipede, in case anyone is looking for a birthday gift for me (coming up in October!).

Send suggestions for improvements!

Update 2016-10-08
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I uploaded a new hexagonal version which I think is the best one yet. Much stronger, easier to p