These probes measure voltage potential on submerged steel structures using a silver/silver chloride reference (half-cell) within a ertacetal body. The contact tip is made from 316 stainless steel. The reference electrode is a sensitive electro-chemical potential sensing device. These units are suitable for ROV use to1500 msw. A shock-absorbing housing is available to lessen the impact in ROV use. It features a connection point for a surface cable to allow the surveyor or supervisor on the surface to monitor the readings. A high-impedance volt meter (<10M ohms) can be used. Replacement half-cells, tips and connectors make the unit fully-serviceable.