The best way to do BTZS testing is with a densitometer, step wedge and the film / developer combination you will work with (please, don't forget the paper). This having been said, there are plenty of other ways to work with BTZS numbers to get good results, it just takes longer, costs more and isn't as accurate. If proper notes are taken and development is known, the same films can be used for a different paper to get results that work.
I've been using a system which does the same thing, but without the densitometer. Although primative, it does a good job. I take a picture and work with the scene as if it were a film test. Take the usual notes on exposure and btzs sbr number, take a couple of shots. Take a guess at development to yield your zones 3 and 7, process and print. Where are the values in the final proof? If there was too much contrast, back it down and do another sheet, if too little contrast, add time. Once you have made this proper development, you have established one point to plot in sbr, time and development.(*** this is a guess at best, certainly not scientific)
While this may not be the correct manner of testing, it gives you numbers which work well enough for everyday shooting. Once the points are plotted, the numbers are "averaged" out with a french curve and you have enough information to do any scene you already know, and a decent way of dealing with contrast and development in ones you may not have encountered yet.
A simple comparison to known values of zones 3 and 7 on a stouffer printed paper strip gives the feedback you need to evaluate the process. As I have said, it is primative, but I have learned quite a bit from this testing method and it has certainly helped me to understand the relationship between exposure, development and the finished print.
I'm sure there must be errors in my process, but don't let the number business fool or confuse you. It may be dry, but the sbr numbers open a world of understanding which I was never able to get from the N, N+ and N- zone system stuff. The beauty of the btzs numbers (sbr) is that it is an exact 1:1 relationship between zones in a print and zones in the film's development. Once plotting is done, you can dispense with any testing and there exists an infinite number of development combinations for any lighting / development scheme you can find. The hard part for me was understanding that a stop of development in the film was much more than a stop of development on the paper. Due to my personal density index (quite high), when the light bulb finally clicked on, it was like a cool shower after too many months without rain. tim
P.S. Please don't confuse the sound of a light bulb clicking on with the sound of a toilet flushing, they are not the same.
