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    Re: Semi-diameter in the Nautical Almanac
    From: Fred Hebard
    Date: 2009 Dec 22, 08:26 -0500

    If I recall correctly,  you have to be about a mile away to use a
    telephone pole and avoid parallax.  The "sanity check" is very nice
    because if you are consistently off, you know either your measuring
    technique is off or there's a maladjustment in the sextant.
    
    
    On Dec 22, 2009, at 7:36 AM, Gary LaPook wrote:
    
    > I like that method of checking index error because you get repeatable
    > results since the variations in the horizon go away. But you don't
    > need
    > to know the S.D. to do it and it really doesn't provide a "sanity
    > check"
    > all it does is give you a measure of the accuracy of the scale between
    > plus and minus about half a degree. This type of check can be done
    > with
    > any far away object such as a building or telephone pole, the actual
    > width of the object makes no difference in finding the index error.
    
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