Bruce,

The ISOP Figure is not important in practice. It states the amount of light (H0.6 in lxs) necessary to gain a density of 0,6logD (ISOP = 1000/H0.6) on the paper. A value of ISOP 500 means, that it requires 2lxs on this paper to gain a density of 0,6logD.

The contrast range stated by ISOR is much more important. It directly states the density range you can copy onto this paper. For convenience, these values are multiplied by 100. If your negative has a density range of 1,0 logD, a Paper with ISOR 100 exactly fits this range. I.e. you will neither loose detail nor will you waste any tonal values.