This may be a stupid question, but if you are contorting yourself to measure your sitbones, aren't they moving into a different position? Or is that only in childbirth?

Second, if one knows one's sit bone width, what does one do with that information? Isn't there still some personal preference as to how your newly mapped sit bones contact the seat? It's not like a shoe where the high point of the arch lines up with the high point of the arch support. Or is it?

I found a saddle I really liked on my third try. And the method was all art no science. On the first two I was pretty conscious of what hurt and why and then I just let my head picture what my butt would like to be sitting on. Browsing in the LBS, I just recognized the contours I pictured, bought it and it's been great. A woman's intuition thing: can't argue that!