Yes, that last photograph supports what I was suggesting was the method that was used to place the cap. The shallow socket would have located the big stone as it was swung around. A monumental feat. Nice to see the workings out. It's certainly moving...
This is the last pic I will show as to 'reveal all' just defeats the object of writing about it with a view to publishing. Here is a clearer view (and I have better ones) showing the knib again. We are on the same wavelength here SG as that is my belief also. If a shallow socket as described was made and the knib used as an aid to line up the capstone, then that would explain why the capstone at that point has broken away underneath as clearly seen from underneath the 'hole'. This would have happened as the sheer weight of the cap began to slip. No mystery attached, pure old-fashioned common sense!
Interesting pics Roy . Tatjana Kytmannow makes the interesting point that Trethevy and Harristown are the only surviving portal tombs with with very high portal stones that have not collapsed .
I was trying not to go to deeply into it at this stage George because of publication but to be honest I was getting fed up with this misbelief that it had never moved. You've seen some of the other stuff I have which I feel backs up my belief...in fact I don't why I say it's a belief, IT HAS MOVED and I know because of my own measurements it has moved again since last year. Since the day the 'mortice' was torn off from under the capstone it has allowed it to move and the closure move out. In time it will go the same way as the others.
Don't bother about the misbelievers and don't waste your pics on them . I imagine for most on here it seems very likely that such a monument will move ,particularly those that have high portal stones and no supporting cairn ,at least as it appears today . The pics seem to confirm this and the EH engineer(s) will hopefully provide the "official " version .