Here is little update

I did following test for Delta 100 (with diffuse head enlarger):

  1. I figured out printing time that gives pure black
  2. Using that time, I printed my test negatives (I used graycard on black background as an test target)
  3. From these negatives I got right negative for zone I, ie. print where I could barely see difference between graycard and black background
  4. Then I checked which negative in my test series give IX that is just off the pure white

So that time (in my case, 9 min, 24°C, DiXactol Ultra) will give N-developing with full tonality scale.
The usable speed for Delta 100 is E.I. 80.

Then I measured densities of all zones. The most important zones were ofcourse zones I and VIII. The zone VIII I planned to use for an reference for testing developing times for N- and N+ developments.

Here is what I got:

Visual (above base fog):
I 0.07
II 0.16
III 0.25
IV 0.36
V 0.58
VI 0.83
VII 1.05
VIII 1.24
IX 1.39
X 1.63

And blue readings:
I 0.09
II 0.22
III 0.35
IV 0.48
V 0.73
VI 0.99
VII 1.21
VIII 1.34
IX 1.51
X 1.69

Does these values sound reasonable?

The suprise for me was how close the blue measurement get to the traditional diffuse reference values for zones I (0.09-0.11) and VIII (1.25-1.35).
Also I was suprised how the visual values are close to the reference values for condensor enlarger (I 0.08-0.10, VIII 1.15-1.25).

Now the big question. Are the reference values I got for zones I and VIII also usable with other staining pyrocathechin based developers (mainly Pyrocat-HD is in my mind).
I guess that they are.