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    Re: Longhand Sight Reduction
    From: Hanno Ix
    Date: 2014 Jun 30, 11:01 -0700
    Greg,

    Well said!

    In my 30 or so sight reductions - not many :(  -  Doniol came out faster than the
    Bygrave, at least than my B-size flat Bygrave with R. Stuart's excellent scales.
    And for Doniol I do not use any calculator, do all the work be hand. In your list
    you did not mention that single multiplication. For that I prefer Vedic since it
    delivers the 4 most significant digits right away. i.e. w/o the need to calculate all
    digits of the product..

    Admittedly, there might be situations where the Bygrave is THE approach
    ( Chichester ) but for the hobby navigator or for a Blue Water CelNav certificate / application Doniol seems hard to beat.

    Nevertheless, the Bygrave still attracts me because of it's sheer ingenuity,
    and building one just for fun is a near term project of mine.

    Thank you for digging up Doniol!

    Hanno





    On Mon, Jun 30, 2014 at 10:11 AM, Greg Rudzinski <NoReply_Rudzinski@fer3.com> wrote:

    Doniol longhand sight reduction summary.

    Pros:

    1. Simple rules.

    2. Easy to memorize.

    3. Uses DR as assumed position.

    4. Fast four place precision.

    5. Flexible for longhand, log, slide rule, or basic non trig calculator.

    6. Works with as few as 2 pages of cosine sine tables.*

    7. Reduction fits on one side of an index card with room to spare.

    8. No form needed.

    Cons:

    1. A few subtraction steps.

    2. Azimuth is not reduced.  **

    * A 6 page haversine table is recommended to save time and reduce errors.

    ** The classic azimuth formula using diagram , slide rule, or longhand to 2 places complements the Doniol Hc formula.

     

    The pros far out weigh the cons making Doniol a leading contender to replace the clumsy NASR at the back of the Nautical Almanac.

     

    Greg Rudzinski

     

    http://fer3.com/arc/m2.aspx/Longhand-Sight-Reduction-Rudzinski-jun-2014-g27966


       
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