VLF means Extremely Reduced Frequency and is identical technological know-how used in detectors developed for cash, jewelry, and relics. VLF detectors broadcast at frequencies measured in kilohertz ranging from three kHz to 70 kHz. Here i will discuss 5 main reasons why you could select a VLF about a PI http://opensource.platon.org/forum/projects/viewtopic.php?p=12846146#12846146