Response to Dev control for b/w films

Doug. I apologise for introducing a tone of controversy into what should have been a straightforward Q & A post.
The answer to your question seems to hinge on where the toe of the D/logE(orH) curve is pinned.
As an ongoing project, I've been transferring the manufacturers rather vaguely drawn curves to a spreadsheet, as and when the need arises. This enables you to get quite accurate density readings from them, rather than just estimating what density base+fog is, or where 1.2logE units from the toe falls.
Anyway, it seems to me that Kodak place their baseline at the point where there is a just detectable upturn in the curve, and put 18% grey 5 stops up from this point. (or 4 stops up from the point where there would be readily detectable detail on the negative)
This fits in neatly with the old 'U' and 'O' settings on Weston meters, and also with the zone system.

Unfortunately, I don't use Plus-x, (I much prefer FP4+) and haven't read the x,y co-ordinates from Kodak's curves into a spreadsheet, so I can't give you any density value. You'll either have to muddle by with a ruler on a printed version, or convert the curves yourself. It also appears that Kodak's 'preferred' development times give sets of curves that fit with the zone systems N, N-1, and N+1 etc. A line through a mid density gives approximately 0.3logE spacings of the curves.

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