Interesting post.
As architect my comment on no.1. is that the north arrow which we place in drawings (at least the ones I place) are based on the North direction on large scale survey maps supplied by planning authorities and on which the drawing would be based.
Errors of 15 degrees are quite serious in this respect, even though one should always take the arrow only as a general indication of north and not for accurate sundial work, for which I would favour four trials (a few days apart) of Waugh's technique from his book.
Best regards
Alex
Malta
1. Architect's Drawings
A typical Architect's site plan includes a very convincing
ornamented letter N enfolding an arrow. The arrow usually
points at some arbitrary angle with respect to the sides of
the paper. Alas, the angle is also pretty arbitrary with
respect to true north. I have known errors up to 15 degrees.
Verdict: Avoid like the plague
