Back in 2000 I wrote an article for Nuts&Volts magazine about predicting earthquakes via a electromagnetic monitor. Back then the EM sensor rotated through 180 degrees taking readings as it went. That was because EM sensors were expensive. Today they are cheap and I am working on a new device that uses 8 sensors in a circle. I am not sure If I should read them or take their difference and read that?
Predicting Earthquakes via Magnetic Field Monitors – [Link]