VLF means Very Lower Frequency and is the same technological know-how used in detectors constructed for coins, jewelry, and relics. VLF detectors broadcast at frequencies measured in kilohertz ranging from 3 kHz to 70 kHz. Listed below are five reasons why you might opt for a VLF over a PI http://gzew.phorum.pl/viewtopic.php?p=607435#607435