Existence of contact between two dissimilar metals in the logging instrument which results in a spurious emf. If electrical [[leak|leaks]] exist between the metals and the borehole fluid, a circuit will be completed in the borehole fluid through which electrical current will flow. Opposite resistive [[bed|beds]], the lines of current are distorted and current flow is confined to the borehole. When this current crosses the SP electrode it distorts the SP [[curve]].