The sum of all the thickness/resistivity ratios of n - 1 layers which overlie a semi-infinite substratum of resistivity ρn, such that S × h1/ρ1 + h2/ρ2 + h3/ρ3 + … + hn-1/ρn-1 (mho), where h1, h2, etc. are the depths and ρ1, ρ2, etc. the resistivities, of successive layers. A knowledge of hi/ρi for the ith layer when it is sandwiched between two layers of much higher resistivity is of importance in resolving the problem of equivalence.
Subjects: Earth Sciences and Geography.