Yeah, a slide rule's supposed to be good to ~3 digits, and I was imagining maybe the crude ones you're hacking up are only good for 2. The one I picked up out of curiosity is a bit sticky in its action, alas, so I haven't been excited about getting into it.

I'd suck at "inventing" anything impressive & practical -- so it'd be hard to get heard about germs, etc., etc., which I do know.