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    Re: Sextant/3 Arm Or Gyro Bearing Pmp Plot
    From: Jeremy C
    Date: 2010 Nov 27, 05:35 EST
    What you gain in accuracy of observation by this method is often lost in the lack of precision in your plotting instruments.  It also takes quite a bit of time to take horizontal sextant observations.
      I have done it, it works, but it is much slower.  All of my plotting tools are indexed to the nearest degree, with eye-ball interpolation good to about 0.25 degrees.  I don't see much use in measuring to the 0.1' of arc for such work.  Surveying is another game altogether.
    In a message dated 11/25/2010 5:30:37 P.M. Central Asia Standard Tim, aruiz{at}orona.es writes:

    See: NP 100 Extracts from THE MARINER’S HANDBOOK Edition 1.1 – December 2009



    I have attached p87&88

    Horizontal sextant angles


    Where great accuracy in position is required, such

    as the fixing of a rock or shoal, or adding detail to a

    chart, horizontal sextant angles should be used when

    practicable. The accuracy of this method, which

    requires trained and experienced observers, will

    depend on the availability of three or more suitably

    placed objects. Whenever possible about five objects

    should be used, so that the accuracy of both the fix

    and the chart can be proved.

    A horizontal sextant angle can also be used as a

    danger angle when passing off–lying dangers, if

    suitably placed marks are available. This method

    should not be used where the chart is based on old or

    imperfect surveys as distant objects may be found to

    be incorrectly placed.


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