I can give a strength of ***this model*** that I bet you never thought of. I graph my curves on paper. And I use a CI transparency overlay to read the graphs.
With more sensitive film, the sensitometer tends to "overexpose" the film being tested when using a 21-step test wedge. Any faster than 400 and I won't have a toe on my graph and I may not even have an 0.1 density reading to gauge speed by.
But my CI index will fit nicely on the graph. So I will know my CI.
***Thought you were talking about CI 'per-se'.
Now that I've printed the chart I know you are talking about something else.
This is same as Zone system except not using Zones at all. Not using N+ or N- either. Just tells you what to develop to if you want to get a print matched to the negative based on your meter reading. Nice. I was going to extrapolate something like this anyway since it is easy for me to develop to a CI.