Thank you Ali23 for your answer, I'm pretty clear with GRmin and GRmax. I cannot get how to read GRlog value from the log.
For example, we need to calculate shale volume in 100 feet section. We set shale and sand baselines to get GRmax and GRmin respectively, but what is GRlog value if gamma ray varies from 40 to 90 and then back to 40 API within the section?
Why GRlog becomes 70, not 50?