When p/z fraction is known but not p and z

[06pg22]

I am seeking to go through a chart/correlation used to obtain p & z when analysis results in p/z answers. Our instructor showed a chart used to obtain z from Ppr/z, but couldn't tell where it was taken from. So pls also mention the reference.

[06pg22]

Worldwide Practical Reservoir Engg Methods, by H. C. Slider
Appendix F
has this plot.

[haminhdung]

In my opinion your problem may be solved as following:
Given some value of P => calculation Z => calculation P' from (P/Z)know=> Abs(P-P') and do the calculation again until Abs(P-P')<e(definition).