OK the arched back ends up being pretty important.

After many years of bending gears with a pair of pliers,

As you turn the pages of the book, the book can actually detect what page you're on, based on the curvature of the pages.

If it had, you'd expect to see a part of the shearedoff cotter pin in one of the holes, or scratches or marks or some bending to show where it had pulled out.

You see the dark line on the side and the top. As you turn the pages of the book, the book can actually detect what page you're on, based on the curvature of the pages.

After many years of bending gears with a pair of pliers, I made that tool, and then I made this other tool for sort of centering gears very quickly sort of developing my own little world of technology.