Measuring your sit bones to help choose the correct size saddle for you is nothing new. But Ergon have up the ante with this digital measuring device. I thought I had a 10cm wide sit bones, actually I'm a 9.8.
I sell saddles. Measuring sit bones is almost a waste of time. As the body leans foreword and aft, which your doing pretty much all the time on a Mtb, the width of area that needs support changes (the pelvis is somewhat V shaped and is obviously wider at one end than the other). This is a re badging of Specializeds Body Geometry theory....which has that same issue.