VLF stands for Pretty Minimal Frequency and is the same technology Utilized in detectors constructed for coins, jewelry, and relics. VLF detectors broadcast at frequencies measured in kilohertz ranging from 3 kHz to 70 kHz. Here's 5 explanations why you could pick a VLF above a PI The depth at https://www.navacool.com/forum/topic/279152/metal-detector-tricks-for-coin-collectors