The set-square metaphor

Some ideas just happen by accident, like the time a few months ago when I facilitated a workshop exercise for a group of senior healthcare managers, and one of the things I'd given them to look at was a scatterplot printed on a sheet of A4 paper, and as I observed them doing the exercise, I noticed that some of them were using makeshift rulers to draw trendlines along the scatterplots, and then using makeshift set-squares to read off the values on the horizontal and vertical axes. I didn't think too much of it at the time, but the image had obviously been subconsciously stored away in my mind. And then last week I suddenly realised that this whole business of using a set-square to get useful information from a scatterplot was a beautiful metaphor just crying out for a blogpost that's - alas - yet to be written.