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    From: Peter Hakel
    Date: 2009 May 14, 11:48 -0700
    After some time I again watched the instruction video that came with my sextant a while back.  Therein the narrator routinely rounds angles to whole minutes of arc at every step of the sight reduction procedure.  This is discouraged by the accompanying instruction manual arguing why would anyone voluntarily lose precision when it's not necessary.  I agree with the latter statement and I diligently keep track of tenths of arcminutes in my own calculations.  However, the fact is that the video narrator (William F. Buckley) himself was a blue-water sailor and this technique obviously worked for him in real life.  After all, there aren't that many steps in the manual sight reduction.  If the round-off errors are a type of a random walk, then we should expect the error in the final result accumulate only with the square-root of the number of steps, times 0.05'.  The systematic and random errors in the sextant sight itself very well may be larger than this rounding in the math, especially in adverse weather conditions.

    Does anyone have any quantitative comments as to how much of an error can be introduced in this manner and whether it has any detrimental effects in practice?  One surely needs high precision navigation when avoiding reefs and such but in that case I imagine that one navigates by reading the waves and water color etc.  CelNav will get you within sight of an island in the middle of the ocean and from thereon you may navigate visually by landmarks, I would think.

    Thanks,


    Peter Hakel



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