Here is another invention that is absolute genius in its simplicity. I refuse to give up my habit of reading printed books despite the profusion of nifty E-readers emerging, and I always have a pencil in my hand for underlining and notes.

This “Constrained Ball” by Giha Woo allows the user to draw lines and measure them at the same time. So it’s not only great for simple underlining, but can be a useful design tool as well.

Found here.