In electrical profiling, a technique in which the spacing of the electrodes or coils is expanded in order to increase the depth below the surface station from which information is obtained. A variety of electrode configurations is used for electrical resistivity sounding and induced polarization surveys. In resistivity sounding, apparent resistivity data are recorded on a log–log plot as a function of their respective current-electrode separations. Master curves are often used to provide preliminary interpretation of the curves, and followed by more detailed and sensitive computer analysis. For electromagnetic (EM) sounding the coil spacing is increased or, in time-domain EM surveys, the frequency is varied. Compare constant-separation traversing.