While in the nineteen sixties, the 1st industrial steel detectors had been developed, and they were being greatly useful for mineral prospecting together with other industrial functions.????? ??? ????? ?? ????????: ???????? ???????? ????? ????? ????????? ?????: ??? ???? ???? ????? ?? ???? ????? ??? ????? ?? ??? ?????? ????? ?????.???? ???? ???????