Rushton,
I used to use the methods you described[which I think are the most well known methods]until a chance encounter with a very nice prominent surgeon in Germany.He has ,to my ears,the best system I have ever heard in My life{and believe me,being married to a Japanese ,and having spent some time in Japan;there are many really good systems there}.Those are the steps that were recommended by him.
You would be surprised at how much easier and faster it would be with the help of SPM,and how different it would be from the Cardas ratio.It always give the most 3-D image,in my experience,and I have recommended the methods[very simple and quick too!!!]to many friends..
Give it a go,and let me know what you think.
CHEERS.