Thank you. Followed your advice and started some thorough search of relevant data sheets. Some further questions please.

In one of the Kodak publications (November 2004 G-21 TECHNICAL DATA / BLACK-AND-WHITE PAPER KODAK PROFESSIONAL POLYCONTRAST III RC Paper) I found some data which I'm trying to understand.

They speak of ISO Paper range, which they define as follows: "These numbers indicate the relative ISO ranges of different contrasts produced with KODAK POLYMAX Filters.The ranges were calculated from the log exposure ranges of the paper. You can use them as guides for selecting the appropriate paper contrast for the density range of a specific negative. When the ISO range of the paper approximately equals 100 times the density range of the negative, the contrast of the print will usually be satisfactory. (For convenience, the log exposure ranges have been multiplied by 100 so that the ISO ranges are expressed as whole numbers.) The contrast you choose will also depend on the nature of the subject."

The table goes as following:
contrast (paper) grade:
-1 0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5+
ISO Paper range:
>150 150 130 120 120 110 100 90 80 70 60 50

From the description Kodak provides it looks to me like I need to divide the ISO Paper range by 100 and the result is the useful density range on the X axis. Is it so?

Yes, I know I'm plotting H&D curves. I was not sure listing lurking time, cameras, or shooting experience makes an interesting introduction, but here goes. Lurked for a week or so, respect the place and read a lot of very interesting stuff on emulsion making. Topic camera now is Zeiss Ikon. Shooting experience with it is 1 year. Born in 1982 in Moscow, Russia. Coming from a family of three generations of photographers. Started shooting when I was about 10. Earning money with photography since 2001. Have a lot of digital stuff. Want to understand why I prefer film. It seems to me that film system is much more balanced, more following physics and physiology. I hope it answered some questions