The way I use the one area test is just as a comparison on myself. For example if I started out at 25% and 2 months later I am at 21%, I know I am improving. (notice I said if. Wish I could see a 4% drop in 2 months, LOL) As for how it compares to other methods, I know the hip area gives me a lower read than my Tanita scale which is really only analyzing lower body fat (which I apparently have more of LOL). They say the most accurate method is the underwater method which is hard to come by and can also have inaccurate results depending on if the person is able to let out all their air each time they are measured. I think the important thing to remember is that what ever method one chooses to use, they should use the same method each time so they can get a fairly accurate comparsion over time.
Jean