Daniel - Barnbaums's habit of placing shadow values atop the barn roof is about as counterproductive advice as I can think of. Where do you go from there? You've already taken up nearly half your straight line already. And that means that there's very little forgiveness at the upper end, and the only solution to a printable negative is gross minus development - the Zone System beaten half to death. Why even bother to meter to begin with if you have to fudge three stops of guess insurance? Playing it safe with a stop of so of extra exposure might make sense when in doubt, but Zone IV ?????? Ridiculous!!!!
I personally like to get the threshold of shadows values above the toe a bit, and find that most Pan films need more exposure than box speed to do that. For example, I rate FP4 at 50. Only with TMax films do I find advertised film speed to work best. But all this is specific-development dependent, so another wrinkle that needs to be ironed out through personal testing.
I also strongly disagree with metering through filters. Just look at the nm spectral sensitivity distribution for various meters. It's never a flat even line, but biassed. Testing for filter factors is easy. Just take the individual filters in question and do a bracket test with 35mm film aimed at a gray card in what you consider typical lighting. Use the factory tech sheet filter factors as a starting mid-point. Make sure your lens and the meter itself aren't aimed toward the sun and affected by flare. Filters do sometimes differ a little from batch to batch even from the same manufacturer, so do test exactly the filter you have in mind for your own kit. And of course, take a reference exposure without any filter at all.
Comparing frames visually over a lightbox is probably adequate for most black and white purposes, though a densitometer reading will be more accurate. An old fashioned trick to make "visual densitometry" more accurate is to take a matte black thin piece of cardboard and paper punch, and punch two hole in the middle of it about two inches apart. Tape your reference exposure (no filter) to the light box and view it through one hole, and leave the other hole for slipping in your respective filter exposures with their bracketed filter factors. If your eyes are rested when you begin, relatively minor differences in density can be detected in this manner.
Personal preferences and the aesthetic application of filters is another topic entirely.
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