Originally Posted by Michael R 1974
Suppose the exposure 6 stops below metered is the first one below metered that yields zero net D, and he decides to start the curve there. The only thing you can say is that this is 1.8 below metered on the relative log H scale, because the metered exposure is the reference point.
You don't even need to have the metered exposure point as a reference on the curve. Put 0.00 at the Δ1.80 log-H and the metered exposure will be at a relative log-H of 1.80. Now you might be thinking that the relative log-H should stand for an approximate actual log-H, but that's not what Henry is doing.

You stopped down 6 stops below metered. It may be that 5 2/3 stops below metered also yields zero net D. Unless you maintain the metered exposure as a reference point, I don't see how you can plot your first non-zero net D exposure at 0.3 relative to a zero net D exposure.
How's it different than the resulting densities from a step tablet exposure (other than way less accurate in the exposure increments)? I still think you're over thinking this. Maybe if you walk through the details of Henry's procedure and point out the part you are having a problem with. And BTW, Henry's concept of speed and metered exposure isn't exactly on solid ground, but that isn't related to the problem you're having.

Film Curve example 2.jpg