How deep reaches a metal detector?
It depends on many factors. Especially on the size of the object and whether the user requires additional information such as the type of metal. For that purpose detectors can display the so called conductivity of the object. To determine the conductivity is only possible on shallower objects. In practice the ability to distinguish between ferrous and non-ferrous items is especially important. Usually small objects like coins are only dug if they can be identified as nonferrous. This is necessary to avoid digging the ubiquitous small iron junk pieces. A high end all purpose detector can locate a coin 20 cm / 8″ deep, a horse shoe some 35 cm / 14″. 90% of the finds are made within 20 cm. That is why many searchers do not even carry a spade but just a pick. 99% of all finds are made within 30 cm. Unusual large objects such as crashed planes can be located much deeper, in particular if a conductivity reading is not required. But these finds are very rare. The deepest object I ever dug was
