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    Re: Say it aint so......
    From: Lu Abel
    Date: 2009 Mar 07, 20:36 -0800

    While I studied for the USPS Navigator grade back when Ageton rather than NASR was the accepted "compact table" reduction method, I do not believe the use of an Assumed Position rather than a DR as the starting point for sight reduction should significantly affect the accuracy of a sight reduction.   The major items affecting the accuracy of a sight reduction (and remember, this is for calculating Hc and comparing it to Ho) is the accuracy of almanac data and the granularity of the tabular reduction data.  For a quick sanity check, consider what would happen if you were doing Law of Cosines with your DR position the same as the assumed L/Lo positions required by NASR.   Would you expect one to be more accurate than the other?

    Lu Abel

    Guy Schwartz wrote:

    Hello folks:

    I am studying for the Navigator grade in the US Power Squadron.

    Part of my sight folder is a two object sight that need to be plotted using law of cosine and using the Nautical Almanac Sight Reduction methods.

    The power squadron has a 3 mile tolerance (GPS location vs. fix position).

    My concern is that the 3 mile tolerance is for both Law of cosine and NASR methods.

    It seems to me the NASR would deserve a larger tolerance in that there are assumed L and Lo positions as starting points

    Am I right?

    Thank you,





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