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    Re: Test your magnetic compass.
    From: John Huth
    Date: 2012 Nov 17, 11:28 +0100
    Remember that the earth's magnetic field is something between 200 and 600 milliGauss.   This is pretty tiny.   Take something as simple as electrical conduit  - even if the AC current inside is shielded, you can get DC ground currents flowing in the conduit that can affect magnetic compasses.  

    I've had this problem with some colleagues with laboratories, where they demand stray fields well below 20 milliGauss.   They expect the University to protect them from these kinds of fields.   I got into heated discussions where I had to tell them it was their responsibility to buck out any stray fields.   At the level of 20 milliGauss, just about any random ground current can create a field of this strength.    

    One of the more amazing things I've stumbled upon are studies that indicate that some birds can sense the earth's magnetic field.   Imagine that - some protein that is sensitive to, say, 500 milliGauss!

    On Sat, Nov 17, 2012 at 7:17 AM, bill <billyrem42@earthlink.net> wrote:
    On 11/16/2012 10:33 PM, Lu Abel wrote:
    2.  Most stud finders work on the basis of ultrasound.

    Perhaps Alex, an apartment dweller is referring to old school stud finders. They had a magnet that reacted to nails in the studs, most likely from nailing/screwing drywall to the studs.

    Bill B

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