How/why does a nomograph work?

When using the nomograph that simga provides (http://www.sigmaaldrich.com/Area_of_Interest/Research_Essentials/Solvents/Key_Resources/nomo_ets.html), I was wondering how and why it estimates BPs for so many compounds so accurately. Was this derived from experimentation with a liquid thats representative of liquids or is there some statistical/geometrical way the graph is drawn. I wasn't satisfied with the "wiki" answer so if there are any scientists out there that know the answer, please so I can stop pondering how this was derived.