Water finder is a geophysical prospecting instrument which uses natural electric field source as a working farm, with resistivity contrasts underground rocks and minerals or groundwater, based on measuring the natural electric field on the surface of the N different frequency electric field component, according to their different variation to study Abnormal changes in geological bodies produce, reaching solve geological problems one electrical prospecting methods. 

Because this method measures the electrical component of the electromagnetic field of the earth, so called natural electric field method; and we chose the corresponding frequency as measured within -50 meters, that were selected frequency, so called frequency selection method, it is always referred to as natural potential frequency method. According to this theory the design and production of equipment called potential frequency of detecting instrument, referred to natural selected frequency electric field instrument or instruments for geological exploration work. Therefore, from a professional point of view to classify, geological equipment should belong to this category in the instrument geophysical equipment among electrical equipment.