I'm about to take up Pt/Pd/Ziatype printing and have been reading Dick Arentz' book. He defines negative Density Range as the density difference between zones VIII and III. Is he referring to a camera exposure Zone VIII, or is he calling his "discernible white" threshold print value Zone VIII and looking at that density on the negative? Ditto on the other end. Is his Zone III also his "useful shadow density" of 0.30 above FBF?