<P> The metal detecting community and professional archaeologists have different ideas related to the recovery and preservation of historic finds and locations . Archaeologists claim that detector hobbyists take an artifact - centric approach, removing these from their context resulting in a permanent loss of historical information . Archaeological looting of places like Slack Farm in 1987 and Petersburg National Battlefield serve as evidence against allowing unsupervised metal detecting in historic locations . </P> <P> Hobbyists often state that professional archaeologists' resource limitations results in the loss or damage of many artifacts by plows, development, erosion and livestock . The language and breadth of legislation regarding artifact collection is also an issue, as the Archaeological Resources Protection Act of 1979 excludes scattered coins, the main target of inland hobbyists . Many hobbyists take issue with the breadth of metal detecting bans, marking large swaths of property off - limits which are either well - documented already or unlikely to ever receive professional attention . Suggestions to certify or offer limited permits for detecting at historic sites have been attempted in some areas of the United States . </P> <P> Recently, productive efforts for cooperation between professionals and metal detecting hobbyists have begun, including the Montpelier Archeology Project and Battlefield Restoration and Archaeological Volunteer Organization (BRAVO) and many more . In these programs, skilled detector hobbyists work with experienced professionals with common goals of accurate, efficient site discovery and excavation . Away from supervised sites, hobbyists using improved record keeping and employment of global positioning system, GIS, logbooks, photo scales and online databases may aid professionals in evaluating possible sites . When searching for a site, hobbyists can aid with electronic scanning, reducing the need for test holes . Some land managers, such as the Tennessee Valley Authority have cited a role for amateur archaeologists in protecting sensitive sites from illegal looting and metal detector hobbyists have aided in the location and preservation of many sites . </P> <P> A series of aircraft hijackings led the United States in 1972 to adopt metal detector technology to screen airline passengers, initially using magnetometers that were originally designed for logging operations to detect spikes in trees . The Finnish company Outokumpu adapted mining metal detectors in the 1970s, still housed in a large cylindrical pipe, to make a commercial walk - through security detector . The development of these systems continued in a spin - off company and systems branded as Metor Metal Detectors evolved in the form of the rectangular gantry now standard in airports . In common with the developments in other uses of metal detectors both alternating current and pulse systems are used, and the design of the coils and the electronics has moved forward to improve the discrimination of these systems . In 1995 systems such as the Metor 200 appeared with the ability to indicate the approximate height of the metal object above the ground, enabling security personnel to more rapidly locate the source of the signal . Smaller hand held metal detectors are also used to locate a metal object on a person more precisely . </P>

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