BTZS Metering Question

I am currently reading the "Beyond The Zone System" book by Phil Davis and I have a question.

He talks about subtracting the low value from the high value and then adding the difference to 5 to give the subject brightness range which is then used to determine the development time.

Example:

If the difference added to 5 = 7 then N development is needed
If the difference added to 5 = 9 then N - 2 development is needed

Question:

If on a very dull day, the difference added to 5 = 5 what would you do in development?

N+2 would be the right development on a flat day when you effectively have 5 stops of Subject Luminance Range when N Normal is considered to be 7 stops.

Quote:

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Originally Posted by Bill Burk

N+2 would be the right development on a flat day when you effectively have 5 stops of Subject Luminance Range when N Normal is considered to be 7 stops.

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Thanks Bill

Depends on the type of paper you like to use. With the advent of high-quality multigrade papers 30 years ago, the need for selective development for each frame can be eliminated. But then I'm a maniac when it comes to checking my filters and eliminating flare in the darkroom. Maybe you use some other printing process, in which case you would need to test and see.
As pointed out, in the 'BTZ system' as described, the scene would need some increase in development time assuming you did not want to or could not print to a higher grade (lower ISO(R)).