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    Re: Latitude of prime vertical sight
    From: Fred Hebard
    Date: 2007 Aug 1, 08:35 -0400

    > Prime vertical observations were treated as special before the days
    > of Sumner and St. Hilaire because they give you longitude. With
    > line of position navigation, there is no longer any need to regard
    > sights taken at the time of the prime vertical crossing as special,
    > because you can get both latitude and longitude from any two lines
    > of position (provided of course that they cross at an appropriate
    > angle).
    Prime vertical and noon shots give you the most accurate fix
    obtainable from two sights, since the lines cross at 90 degrees.
    There isn't much increase in accuracy, however, compared to lines
    crossing at, say 60 degrees.  And three sights are better than two
    given adequate spacing.
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