My favourite part of the entry is that it lead me to the discovery of the UK Roundabout Appreciation Society. Never change Britain.
https://en.wikipedia.org/wiki/Roundabout_Appreciation_Societ...
https://en.wikipedia.org/wiki/Roundabout_Appreciation_Societ...
I haven't read it for a while, but I think there's an explanation in the book from the printing company -- they wanted to test out their new colour printing press, so sent someone round the industrial estate with a camera and made a calendar. Potential clients were given it as a sample, but they then received requests to purchase them, and eventually made the book.
[1] https://books.google.dk/books/about/Roundabouts_of_Great_Bri...