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    Re: 3 Lop's
    From: Joel Jacobs
    Date: 2004 Nov 15, 16:29 +0000
    In addition to Fred's and Frank's reasons for a taking a round of sights using three bodies, let me add that the navigator's preception of the horizon will vary with the direction he is facing. This will make a differnce in the altitude he measures. For all the reasons, a three sight fix it recommended by many.
     
    Joel Jacobs

     

    -------------- Original message from Frank Reed <FrankReedCT{at}AOL.COM>: --------------

    Alex E asked:
    "Can anyone explain, under what circumstances one could
    possibly want to determine her position from 3 LOP's?"

    Fred H already gave a nice account of the issue of dip variability. The "triangle fix" also helps to uncover any other fixed systematic error in clearing altitudes. For example, suppose my index correction is -1.5 minutes. I plot my three lines and discover a triangle that's almost 6 minutes across. That's such a large error that it would lead you to take a closer look at your calculations. In the case I'm imagining, you might discover that you applied the index correction with the wrong sign, adding instead of subtracting it. That would push each LOP 3 miles away fro! m the vessel's real position. By contrast clearing three sights each of two objects would not reveal this sort of error.

    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
       
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