I’m sure no one’s thought of this idea before – turning an ‘analog’ ruler into a digital one – but Shay Shafranek has done exactly that. Taking a circuit board, he placed a set of LED digits under a thing strip of wood-like material and added a reset button and little touch-sensitive buttons on the side to detect where the pencil is. The beauty of this is that it can do everything a normal ruler can do, except better of course! Drawing lines of exact length are instantly more accurate with a digital scale, the ruler can help scale drawing by setting it into scale mode (1 unit on the ruler = x units on item) and measuring long distances are easier as the ruler will add up each individual distance when it’s moved!
I think I’d be happy to pay a crazy amount for a ruler like this, but unfortunately it doesn’t seem to be for sale at the moment. In the mean time, there’s a really good presentation of what the ruler can do over at ShayShafranek.com.