What does "ISO range R" mean in the Fomabrom paper spec sheet

bonk

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In the spec sheet for the Fomabrom paper (link) there is table that list the "ISO range R" next to "ISO speed P" for the various gradations.
What does "ISO range R" mean? I have read Kodak Basic Photographic Sensitometry Workbook but still can't quite understand what "ISO range R" refers to.

 

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koraks

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It's the contrast range.

Paper Grades | Roger and Frances

At their most basic, paper grades could hardly be easier to understand or to master. Paper grades range from 00 (very soft) to 5 (very hard).
www.rogerandfrances.com
Scroll down to 'the numbers'.

Have fun; it's a useful page, that one.

PS: I really like that paper. It tones very nicely for a neutral tone emulsion. The only drawback IMO is that the surface texture is decidedly less refined than e.g. Ilford's.
 
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bonk

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Ah, so it is just some sort of standardized way to define the actual "grade" of a paper? Did I get this right?
 

albada

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As koraks said, it's the "exposure range" (I think that's the correct term) of the paper. That number is the amount of exposure needed to change almost-white to almost-black on the paper. It's actually the base-10 logarithm multiplied by 100. Yes, it's an objective (standardized) measure of actual contrast.
 

Bill Burk

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It’s logical to use too.

The right paper grade ISO R number is one that’s close to what you get when you use a densitometer and take the difference between the most and least dense significant parts of the negative you want to print, times 100 (in your head just ignore decimal place).
 

ic-racer

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ISO(R) is the logarithm of the exposure range required to give a full tonal range, expressed to two significant figures, with the decimal point removed. Typical figures might be Grade 5 = ISO(R) 40 to 45; Grade 4 = ISO(R) 60 to 70; Grade 3 = ISO(R) 80 to 90; Grade 2 = ISO(R) 100 to 110; Grade 1 = ISO(R) 120 to 130; Grade 0 = ISO(R) 140 to 150; Grade 00 = ISO(R) 160 to 180.
 

ic-racer

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For example with a 21 step wedge (0.5 stops, or 0.15 log d per step) one can count the number of gray bands and get the ISO(R).

4 bands = 4 x 0.15 = 0.60 = ISO(R) 60 = Grade 4 etc.
 
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