That page doesn't actually state anywhere when the term 'turns' was actually introduced, the concept yes but not the terminology. As far as I can tell the first

That page doesn't actually state anywhere when the term 'turns' was actually introduced, the concept yes but not the terminology. As far as I can tell the first references it gives to the term being used is in ISO 80000-3:2006, completed in 2009, although it must have existed earlier because Fred Hoyle appears to have used it and derivatives in 1962. I thought the reference to percentage protractors might be fruitful, but I tracked down the article reference for that from 1922 and it doesn't use the term.