Numbers can be misleading -- they don't take into account that a person's form can be more elliptical or more round. I am extremely elliptical -- I'm wide in the hip but little booty, so I might measure more hourglassy but appear slightly pear-ish when viewed from the front, an angle that also tends to not show how busty I am. When I turn to the side, I look more top heavy because I don't tend to carry weight in my stomach.
I also think that being short- or long-waisted can play tricks on the eye when it comes to these proportions. So, yeah, numbers can be helpful, but I think a mirror and photo with a close-fitting outfit method works well too, as long as the photo is taken from the proper angle and distance so the image is not distorted.
