Very low frequency (VLF) instruments have been used since the 1960s. The EM16 was the first instrument manufactured by Geonics, Ltd of Mississauga, Ontario, Canada. It was used for many geophysical surveys that found lots of big mining targets. For many years the Geonics EM16 and the ABEM Wadi were the VLF instruments used all over the world. The only current VLF instrument is the GEM Systems Walking VLF, which is a three component VLF sensor combined with a magnetometer. The older instruments required orienting the sensor at each measurement point relative to the orientation of the field from the VLF source. VLF data can be used to generate electrical resistivity profiles to depths of potentially 100 meters. It is not a method to detect small, shallow targets. It can be used to detect large or linear conductive targets.