The history of graph paper, from Alexandre Borovik's Mathematics under the Microscope.
I often find myself thinking that graph paper is an innovation whose time has passed. Its main purpose, in my life, is to make my students' homework harder to read; there are some of them who write on graph paper despite the fact that we are very rarely asking them to graph something by hand, and the vertical lines end up distracting my eyes. And on those occasions when I do want to graph something, I use a computer.
Similarly, I can see how graph paper would be useful for numerical computation, because it makes it easier to line up the digits of various numbers one wants to add or subtract; but I use a computer for that, too.
There was a time when I was playing around with tilings of the square lattice a lot; during that period I liked graph paper. In the same vein, a few days ago Borovik illustrated multiplication of the Gaussian integers on (a simulation of) graph paper.