[Stupid Product Idea] Gradient Ruler
The gradient ruler is a length measurement tool, whose increments become successively smaller towards one end. Basically, it's a normal ruler one would find in a stationary store with a total length of ~30 cm. The catch is that the distances between successive lines are asymptotically small towards one end. At lengths below 1 mm, one will probably need a microscope to tell the difference. Even smaller scales would need photo-lithography to be manufactured. You may wonder, why would anybody need such a device. It could be used to illustrate the fascinating scale to which our knowledge of the universe extends. That's pretty cool.