Gauss Meter in Use
In the photo above you see me with the gauss meter set up against a fairly large primary battery cable on a boat. As I recall I had a circuit activated that was pulling around 8 amps through the wire. The meter is showing a field strength of 2.5 milligause. Not much you might be thinking, but by replacing the gauss meter with a small hand-held compass, I was able to induce about an 8 degree deviation on the compass at the same distance from the wire.
To establishthe zone of separation, simply activate a circuit and put your meter right up against the conductor supplying the electrical load. Then slowly pull your gauss meter away from the wire until the meter reads 00.0 milligauss. Whatever the distance away from the wire is that you achieve that reading is the safe zone of separation for magnetically sensitive devices like autopilot direction sensors and steering compasses.
Use the tool around appliances to establish the safe zone. Things like battery chargers, inverters, windshield wiper motors (any electric motor) can be very powerful emitters of electro-magnetic fields.
I got my meter at: www.professionalequipment.com