Aargh, just updated to Firefox 21 and those tweets do not appear. Only get to see either a thin line or a large-ish empty box.
The link at the top of the article is stuffed ;)
Why does the "Goodness of Fit" explanation talk about "R^2" but the table above it talks about the "r value" - or are these unrelated?
Geoffrey Whitehead's letter can be found here