VLF stands for Quite Lower Frequency and is the same technologies used in detectors developed for coins, jewellery, and relics. VLF detectors broadcast at frequencies calculated in kilohertz starting from 3 kHz to 70 kHz. Here are 5 explanation why you would possibly choose a VLF more than a PI https://www.cyberlord.at/forum/?id=11711&thread=2396