A [[resistivity]] measuring system using a "lateral" [[electrode]] configuration. A constant current is passed between an electrode A on the [[bridle]] and a distant electrode B, while the potential difference is measured across two electrodes, M and N, located on the [[sonde]]. The MN distance is small compared to the [[AO spacing]], which is the distance between the current electrode and the midpoint between the [[potential]]-measuring electrodes, typically about 18 feet 8 inches. A short lateral sometimes uses a spacing of 6 to 9 feet. The potential electrodes described above are located below the current electrodes, but on the [[reciprocal sonde]] the functions are interchanged so that potential electrodes are above the current electrodes. The [[measure point]] is the midpoint between the two electrodes separated by the shortest distance (i.e., MN electrodes; or, AB electrodes on the reciprocal sonde).

The lateral device has a deeper depth of investigation than the [[normal device|normal devices]] with which it is generally used, but has the disadvantage that it requires thick homogeneous [[bed|beds]] for optimum usefulness and produces an unsymmetrical [[curve]].

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