Electronic apparatus and instruments for locating metallic and non-metallic objects in the ground, in cavities and underwater; data processing equipment and computers, in particular for use in the evaluation of data from positioning apparatus for locating metallic and non-metallic materials and cavities; archaeology apparatus and instruments; batteries and accumulators; observation instruments; computer operating programs, recorded; magnetic and optical data carriers; detectors; holders for electric coils; altimeters; interface apparatus or interface programs for computers; metal detectors for industrial or military purposes; radar apparatus, in particular ground radar apparatus