Four electrodes are placed in a straight line at equal spacing. The instrument introduces current through the two outer electrodes and measures voltage between the two inner electrodes. The measured resistance and array geometry are used to calculate apparent soil electrical resistivity.
The crew repeats readings at planned spacings, stations, and orientations. Increasing spacing samples a larger earth volume, but spacing is not an exact depth. Layered ground, buried metal, grounding conductors, overhead lines, limited geometry, contact resistance, and electrical noise can affect the response.
Calicore reports station coordinates, alignment, spacing, measured resistance, calculated apparent resistivity, units, current field condition, photographs, deviations, and limitations. ASTM G57-20 and IEEE 81-2025 are common technical starting points; the project specification and receiving engineer control the final scope.