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    Re: errors in plotting and a possible/partial fix thereof, as menti...
    From: Gary LaPook
    Date: 2010 Dec 29, 11:40 -0800
    If you are looking at my explanation of the use of the MOO table that I posted here


    remember that I my explanation the sign of the correction, a minus for bodies ahead and a plus for bodies behind, are for corrections to be applied to the Hc not to the Ho. In aviation you precompute the Hc and then adjust it for MOO and motion of the body and you also apply refraction to the Hc with the sign reversed to arrive at Hp, precomputed altitude. Since you use the marine practice of making adjustments to the Ho you should use the signs in the MOO table in H.O. 249, plus for bodies ahead and minus for bodies behind, These are also the signs I used in the tables that I computed and posted.


    --- On Wed, 12/29/10, Gary LaPook <glapook@pacbell.net> wrote:

    From: Gary LaPook <glapook@pacbell.net>
    Subject: [NavList] Re: errors in plotting and a possible/partial fix thereof, as menti...
    To: NavList@fer3.com
    Date: Wednesday, December 29, 2010, 11:14 AM

    Jeremy wrote:

    "If I am using the GPS fix as the AP, I first have to advance and retard each of the stars along the track line. The trouble then becomes that I have such small intercepts it is difficult to mark them accurately (my normal dividers leave a 2mm gap between points). My other dividers have much larger points which are also not as accurate. Then I have to spin the triangles from the azimuth to the LOP angles and i always get a bit of error trying to get the exact distance from the AP. Do this over 5 stars and so, and the error just starts to compound."


    Jeremy, look at my prior posts on mathematically advancing LOPs. In addition to the tables I posted you can also use the Motion Of the Observer table in HO 249, just divide the speeds by one hundred and the corrections by one hundred. For eighteen knots just double the 9 (900) knot correction. The table I posted goes up to 15 knots but you can calculate the values for higher speeds and make you own table.


    15 knot table




    Five minute table for eighteen knots:





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