This article is fundamentally about the calculations behind the ways in which computers draw graphs. In the era before computers (unknown to most of you, but very familiar to me!) graphs were drawn on paper. Typically, the data points were plotted.
Let me begin by recounting a story I first heard almost fifty years ago. This is, of course, a long time and over the intervening years I have lost contact with the people involved. So it may well be that I have misremembered parts of it and the actual event may well have been somewhat different in its details.
Many readers will at some time have played games with a pack of cards. In most games one begins by shuffling the cards so as to randomise their order. There are various different ways of shuffling, one of the most popular being the riffle shuffle.