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    Re: Automatic deviation calculation by electronic compasses
    From: Frank Reed
    Date: 2009 Dec 9, 22:51 -0800

    Digital compasses today certainly include the ability to generate their own 
    internal calibration tables. I've seen this in action on a new iPhone. When 
    it needs to re-calibrate, a little notice comes up with a graphic telling the 
    user to wave the phone around in a figure-eight pattern. And no, I have no 
    idea how that works, and I think that's a big part of the problem in these 
    discussions. NO ONE on NavList knows how these devices work. But if you would 
    like to wrap your brains around this issue a little more, despite being 
    technically off-topic for our traditional navigation group (not a complaint, 
    merely an observation), have a look at the technical specs on this rather 
    pricey little digital compass chip from PNI:
    http://www.pnicorp.com/products/family/fieldforce/tcm-xb
    Apparently, for a thousand bucks per chip, you can get a pointing accuracy 
    (after a certain calibration sequence) of 0.3 degrees r.m.s. If you browse 
    this site, there's lots of interesting talk about calibration in various 
    conditions and it seems at least somewhat clear to me that they do all of 
    this by detecting field gradients, however the details usually end with the 
    phrase "proprietary algorithms". 
    
    -FER
    
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    NavList message boards: www.fer3.com/arc
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