VLF means Extremely Very low Frequency and is similar technology used in detectors developed for coins, jewelry, and relics. VLF detectors broadcast at frequencies calculated in kilohertz ranging from 3 kHz to 70 kHz. Listed below are 5 explanations why you may perhaps go with a VLF about a PI http://taniecirlandzki.phorum.pl/viewtopic.php?p=117863#117863