Gradiometer (seismic) : A device that measures an electric field at multiple points at the same time. The gradient is the difference in measured values per unit of distance between the measuring points
George E. King Engineering, 5000 Oilfield Terms: A Glossary of Petroleum Engineering Terms, Abbreviations and Acronyms, US 2010. http://gekengineering.com/Downloads/Free_Downloads /Glossary_of_Petroleum_Engineering_Terms_25_August _2010.pdf, (Oil - Amer) {593}