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    Re: Horizontal Sextant angles plot.
    From: John Brown
    Date: 2010 Dec 1, 13:42 -0800

    Byron wrote:

    "I am pleased the way that the Horizonta Sextant grid is well known.........What are your answers to selection of Navaids?"

    The main criterion is that the navaids and the observer should not lie on the arc of the same circle.

    The Admiralty Manual of Navigation, Vol 1 (1987 revision) goes into the geometry of Horizontal Sextant Angle (HSA) fixes in some detail, including a comprehensive discussion of errors in appendix 7.

    Important factors are the acute angle of cut of the arcs, the distance of the fix from the middle object, or object common to both observations and the mean of the ratios r1 and r2. r1 and r2 are best described in the attached file.

    The error in the fix will be least when three conditions are fulfilled:

    1. The distance from the fix to the middle object is as small as possible.
    2. The angle of cut should be as near to 90 degrees as possible.
    3. The mean ratio should be as small as possible.

    Any two of these conditions should result in a reliable fix.

    Regards to all
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