This might be a more general answer than what you asked for, but the Zone System essentialy stands between a pure sensitometric approach, perhaps exemplified by Phil Davis' Beyond the Zone System, and an approach which just relies on experience and knowledge of one's materials. If you want all of the data, then you'd better get a densitometer and plot curves for your film, but also for your paper, because doing one without the other doesn't make sense.(posted 8515 days ago)Personally, I do not feel the need to do this. Studying the Zone System has been very helpful in getting me to understand how the film works, but I now take a very simplified approach. It consists of ONLY finding the ISO fo any given film and developer combination by shooting a few frames on Zone I and then printing them, using my standard paper, paper developer, and filter setting.
First, I shoot 3 or 4 frames at around the ISO which I think the film will be and develop it at a standard time which the manufacturer, or others have recomended. Then I find the shortest printing exposure that will yield maximum black for a blank frame (fb+f), and use that enlarger exposure to find the first frame Zone I frame that will give me a hint lighter than maximum black. This is my ISO for that development time. It takes into consideration my film, paper, developer, etc. I don't worry about finding Z 5 or 8 or whatever. This just comes with experience. I know what a contrasty neg. and what a flat neg. and what a normal neg. is when I print it. I intuitively find the times for pulling the film or pushing it approximately 1 zone or two zones. Even if you determine sensitometrically what an N+1 development is for example, nothing guarantees that your eye will know exactly that this or that part of a picture should be pushed from exactly zone 7 to zone 8, and not zone 8.25. Plus, your meter, shutter speed, thermometer, will all have small margins of eror.
The advantage with my approach is that with a new film-developer combination, I can go out and shoot some shots on the film, leaving only 3 or so frames for exposing a gray card (or in my case a calibration device which you can find on circada.com) at Zone I. For example, in the case of Delta 400 in XTOL, I might guess that the ISO will be either 250, 320 or 400, so I just expose for Zone one for these three settings. With 3 frames, I have a starting point, and when I print the negs, I can judge if this particular time resembles my normal, or maybe a normal minus one-half, or whatever. The next film I shoot, I might develop at a corrected time, and if this time is significantly different, retest the ISO using three frames of that film.
To me, this is the minimum testing necessary, and allows me the most time to just shoot and have fun, and it allows me to try out new film developer combinations without doing extensive testing. But each one has their own way. Good luck.