The window-cleaner analogy is very good. Is that an original? (Btw, very impressed at the speed with which you're constructing this tutorial without sacrificing quality) --Laird (talk) 04:17, 9 April 2015 (UTC)

The analogy is original as far as I'm aware, yes. --Rjh (talk) 04:35, 9 April 2015 (UTC)