The things on the German ruler, and to some extent Dave's, would be better served printed single sided on acetate (or a more modern equivalent). Easier to lay the footprints over the top of a PCB to see what size they are. Maybe the ultimate version would have several, pinned together at one end like a set of feeler gauges. That would free up more area to include all the good ideas that everyone has come up with. And to do things like showing voltage spacings physically, so you could put the ruler over a board and see directly what voltages were supportable.
It would help in resolving a fundamental conflict with this ruler, which is trying to be two things - a measuring device and a pocket reference.