Magnetometer??

Greetings All,
does anyone have an operational magnetometer on their plane. I would like to
find out the distances from electrical wire and ferrous bolts and nuts. The
installation notes has wording like "As far as possible", "Not too close". I
thought for a second that I was talking to my Ex.... If anyone could give
me distances in feet and inches I would really appreciate it, I want to
place the mount in the wing before I finish closing it up. Thanks for any
help you guys can give.
david