I've just found (and read) this excellent page from the wiki, and I have a couple of questions.
When I was first trained in the noble art of framing some nine years or so ago, I was shown a method for tying the cord/wire which I've used ever since. It now appears from the article I've just read that I've been 'doin' it wrong'

My questions are these
A) Do you mark the back of the picture to show the 'hanging point(s) for the customer (if so, what 'hanging angle' do you use, 60 degrees would seem best for heavier frames?)
B) How far 'down' the frame from the top do you position the 'D' rings ? (assume that's the preferred method for this exercise)
C) How far from the top of the frame do you keep the cord ?
Thanks in advance
<edit> Sorry - just thought of a 4th.... D) At what overall weight would you begin to recommend two hooks, even if the cord being used would support a single hook?