I'm sorry for being off the current topic but I have a questions regarding film test based on WBM in general. I tried to read all threads about the subject but still a few aspect of the method are not clear for me.
I'm referring to the method described in the WBM 2nd edition pages 214 - 224 and pdf document + xls spreadsheet ( http://www.darkroomagic.com/DarkroomMagic/Darkroom.html Film test procedure)

1. Exposure
I'm using 31 steps stouffer transmission projection step wedge, size like 120 film

Photographing step wedge using window, light table or slide copier (I'm aware about flare issue etc)

What would be the best way to measure correct exposure? Cameras I'm using do not have built in light meter. Take a reading from diffused "light source" (window, light table, slide copier) without step wedge and use it as exposure? Should it be adjusted or use exact light meter reading? or maybe take a reading with step wedge in place - which part of the step wedge should be used to read exposure (120 size step wedge is quite small)?


2. Densitometer (how to read densities for development time tests and effective film speed test)

In pdf document I found on page 4:

"My densitometer has a calibration
button to ‘zero’ out the measurements,
because it does not have an internal light
source of known intensity for transmission
density readings. In other words, it
can be used with different light sources
and allows for relative and absolute density
measurements. If your equipment has a similar feature,
then take the first reading with nothing in the light path,
push the ‘zero’ button, and then, continue to take all the
measurements.
This will enable you to measure the ‘base+fog’
density of the test negatives. If you ‘zero’ the measurements
to a blank piece of the film before taking any readings,
then all base+fog densities are equalized, and you would
be unaware of any fog increase due to development time.

but on the same page there is a Fig. 3 (please see attached) where densities for test negatives starts from 0.02, 0.03 therefore (in my opinion) could not be measured with densitometer zero out with nothing in the light path.

Also on the page 4. (pdf) there is a Fig. 4 (attached) which shows D min = 0.17 - is it 0.17 above base + Fog? Should densitometer be zero out on base + Fog or with nothing in the light path to correctly read film speed test?

Should I zero out densitometer with nothing in the light path or on film base (in case of step wedge on step 1 ?) ?

thank you
Tomasz