Helen, I agree you have a nice avatar. While what I am about to say doesn't directly respond to Alex's original question, it does relate to BTZS as I understand it.
Originally Posted by Helen B
The major difference in the BTZS as opposed to just taking an incident meter reading of the object or scene is that the BTZS begins by determining the characteristics of the paper. That is something that Ansel Adams failed to adequately address in his formulation of the Zone System.
The way that I have determined the characteristics of the paper is by contact printing a step wedge (such as a Stouffers) onto the paper I am testing. Next I develop the paper as normal. When the paper has dried, I read the reflection densities of the steps on the paper. From that I am able to determine the exposure scale of the paper. When I determine the exposure scale of the paper then I can determine the appropriate exposure and development times of the film to give me the appropriate density range on the negative to match the paper.
I have found that since I started using this system that my negatives print easier and my prints are more in keeping what I want.