There are actually several sites and many books that discuss personal film speed. Know because I went through this earlier this year, it is not hard to do, but requires preparation, attention to details and burning some film up on test shots. Les, I don't feel that you were plugging your book at all (keep looking for it, quess I will have to order it)..the whole concept of a personal EI is something some grasp and other do not - at leat right away.
Since I do not have Les's book, I can't say if his explanation is easier than some of the ones I have seen...some become way to complicated. LooK around, find an explanation that makes sense to YOU and then go for it ...it is the basic building block for exposure/film development and printing.