biscuit74,
I've been following the thread and its drift with a great deal of interest, and I'm pleased to have contributed in a very small way to Pprune. (I used to help out a bit in the computers & internet forum but every time I go there now, there seems to be a bunch of competent and well-informed regulars taking care of things).
As a side-comment, the "two mistakes high" rule can be usefully applied to many non-flying situations as well.
Thanks to all.