VLF means Very Very low Frequency and is identical technology used in detectors designed for coins, jewellery, and relics. VLF detectors broadcast at frequencies measured in kilohertz starting from 3 kHz to 70 kHz. Listed below are five explanation why you might opt for a VLF about a PI The https://archives.profsurv.com/forum/Professional-Surveyor-Magazine-Discussion/Education/-151484.aspx