I don't think anything had to be explained sundog; as I said, a bit of lazy writing on my part for which I apologise. However, from the OP point of view of measuring a 3" blade for a non-locking knife (as the thread is titled) - i.e. a knife one can carry without quoting the 'good reason to carry' reasoning as long as one was not displaying any 'intent', locking Opinels would be illegal.
Anyway, I suspect we all agree in principle, the letter of the law is ambiguous and the detail which we are discussing is not well tested by case law. My every day carry (as in it is always in my jeans pocket) is a non-locking, two handed opening, pocket knife with a blade length of 70mm measured from the tip to the end of the scales (method A) and it does everything I need on a daily basis. I carry different knives when I have good legal reason to do so
. By using that method of measuring I am happy I stand on the right side of the law without ambiguity or discussion.