Gosh. I knew the moment I asked the question I was going to get so much more information that I could deal with! But I do appreciate this summary of points. I had guessed that different people might use different criteria because well, that's just life. But now I have some names to think about...

I'll have a loot at Nettl. He sounds like a sensible chap. Does he include eg the Scottish/English border within his pessimism? Is it down at that level? And would this not challenge Bayard who seems to be working on a cross Atlantic and therefore National boundary level. Are these sensible questions, even.

I am very new to this 'tune families' way of thinking. Nut it has caught my interest. So please be patient.

Thank you for the response