The A Din classification that we have currently was proposed by the Leyline man - In 'An introduction to Bibliography for literary students' by Ronald B. McKerrow publ 1927 Clarendon p108

'Mr Alfred Watkins of Hereford has pointed out that if paper of sides of an original sheet are proportioned 1 : sqrt{2} (square root of 2), then however one folds it by doubling, the proportions of the resulting leaf are unchanged, and this proportion is an excellent one for most kinds of books'

I don't know if this is generally known about Watkins, or have I just stumbled across this evidence in this 80 year old book - or even if it was proposed before Watkins, but I am jolly impressed - despite my inability to find sqrt{2}