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    Re: Watch into Compass?
    From: Dan Allen
    Date: 2004 Feb 12, 19:54 -0800

    On Thursday, February 12, 2004, at 07:45 PM, Frank Reed wrote:
    
    > "I think the accuracy is much better, probably within five degrees and
    > most of that is from casually pointing the tiny watch hand at the
    > bright spot in the sky."
    >
    > Sometimes yes, but other times, no way. You should also try it
    > "double-blind" sometime. Find yourself a kid "who doesn't know any
    > better" and teach the trick. Then go out somewhere, spin said kid
    > around until dizzy, and then try to have the kid find the compass
    > directions. No coaching! How far off are you and your navigational
    > guinea pig?
    >
    > Until you have procured your guinea pig, consider this: in most of
    > June and early July, the Sun's declination is within a degree of 23.
    > For that dec, the Sun's azimuth in your latitude (you said 43 N)
    > reaches 270, due west, at about 4:10 (-ish) local apparent time. If
    > you try the watch trick at this point, it will tell you that South is
    > close to azimuth 209. That's pretty far off already. This ignores
    > equation of time and zone correction which could easily add another 10
    > degree error on top of that. So that's possibly 39 degrees error in
    > direction for an observer well away from the tropics. It's worse
    > farther south. Yes, it's very roughly in the right direction, but I
    > think you would agree that it's not much better than you would get by
    > guessing. A person who knows the Sun rises generally in the east and
    > sets generally in the west wouldn't be much farther off under these
    > circumstances than someone using the watch trick. It's not a very good
    > compass!
    >
    > The watch trick works reasonably well whenever the Sun is close to the
    > meridian, and it also works reasonably well whenever the Sun stays a
    > long way from the zenith. Otherwise it can be waaay off.
    
    Thanks Frank.  This is what I had thought I had heard.  I wonder why
    the US still teaches this to its troops then?
    
    Dan
    
    
    

       
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