I have some questions about the Koenigsberger ratio that relates induced and remanent magnetization in rocks. I have not had a chance to take a course in petrophysics and have a hard time finding detailed information online.

The general equation is easily found, I guess, but the details about assumptions, approximations and the induced field to use etc. is seldom explained.

Q = NRM / (K * H)

where NRM is the remanence in [A/m], K is the susceptibility in [SI] and H is the inducing field in [A/m].

What assumptions and approximations are used for this equation to hold?

I've often seen that H in the equation above, is approximated to 40 A/m (roughly 50265 nT), which simplifies the calculation. But is this approximation widely used and acceptable? It gives up to 10% error in for example northern Europe, if one compares with using IGRF values for the inducing field.

Furthermore, I was told that it is the inducing field at the time and location of sampling that should be used. However, I feel that is a bit odd and rather think it should be the inducing field at the time and location of measuring the magnetic properties of the rock sample, so that all values in the calculation correspond to the same time and location. So, what is the correct answer here?

I don't have oriented samples, so I'm generally not considering directionally dependent factors, however, it would be interesting to hear if also that plays a role in determining Q.

I would very much appreciate if someone could help shed some light on these questions!