Actually I was
referencing the nomograph on p. 140 of WBM. There is a similar version of it on p. 66 of Stroebel's book "Basic photographic materials and processes
" (p. 66 here)
(which in turn was taken from a Kodak Publication from 1976) but the neg density ranges that nomograph lists differ from the one in WBM by quite a bit. e.g. the ISO std CI of 0.57 (in 1976) matches a neg dens range of 1.05, but in Ralph's nomograh the ISO std of 0.58 matches a neg. dens. range of 1.29 (which I rounded up to 1.30 and used that in the formula I gave above.
Now why do the two nomographs differ so much ? I think it is because Ralph made a different assumption than that in the footnote (*) of p. 66 which reads "these are the typical negative density ranges that result when normal luminance range subjects (7 stops range) are exposed with moderate flare level lenses and developed to the contrast index shown in the left scale