I needed calipers longer than the standard 17cm for an upcoming bike project. I happen to have an old Logarex ruler laying around that's more than long enough.  An idea struck and so I present to you: Caliperuler. One jaw is fixed, one slides freely until tightened by the bolt. The measuerement can be read between the jaws on the scale. 

Could you just use the ruler? Maybe. Is this better? Maybe. Is it more fun? Certainly.