Howdo Wideford
I struggle with gateposts in my own area, some seem to scream out 'standing stone' ,but when you sit down and analyse their location, obviously aren't. I guess this must be an even greater problem in the Orkneys where you have a 5 thousand year unbroken tradition of using stone where we on the mainland would have used wood.

Does it not strike you as being a remarkable coincidence that this specific pairing are exactly the same size as a modern farm gate? I'll lay odds that the gate is also situated in a good place in the field to have a gate.

"By contrast the makers of the f.f.a.s. went out of their way to choose contrasting shapes"
"Usually only one has an obvious lined socket. "
Could this not be evidence of a time gap between the pairing of the stones - a more recent stone being paired-up with an existing, socketed stone?

"And with all the cases I have seen they do appear to be in the right place for dividing up territory."
Could this not be a definition of most field boundaries both ancient and modern?
How much of an effect did the Acts of Enclosure have on the Orcadian landscape?

cheers
Fitz