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    Re: Using the Anti Spoofing App
    From: Steve E. Bryant
    Date: 2019 Jun 11, 12:48 -0500
    Thank you, thank you John!
    Frank is so incredibly busy; I knew my only hope would be from knowledgeable members of this group!  

    Steve OCBC
    PS: I haven’t taken the time yet to attempt to digest your comments; but, I do greatly appreciate your reply. I’m certain I will benefit from them!

    Steve OCBC
    35 33N 97 37W
    PS:  there used to be a means, whereby NavList participants could engage in independent email conversations.  Do you know if that function still exists such that one could opt in or out of it ?

    Sent from Steve's iPhone

    On Jun 11, 2019, at 12:02, John D. Howard <NoReply_Howard@fer3.com> wrote:


    I cannot answer all your questions, only number 5.

    a. Sea horizon is easy, as you said. It will require a Height of Eye above the water. HOE will then figure the dip.

    b. Bubble is for us that use an aircraft sextant. Aircraft sextants use a bubble to determine the level - put the sun ( or star ) in the bubble. No HOE needed nor dip.

    c. A mirror artificial horizon is used inland ( to practice ) with a marine sextant. The angle that the the sextant reads is twice the normal angle so the App will show twice the normal angle.  No HOE or dip. The distance to the mirror does not matter.

    d. True horizon is defined as 90 degrees to down. Some of us use a theodolite to measure the sun and stars. Any instrument that is leveled with a plumb bob or gravity uses the true horizon. No HOE or dip.

    e. Geocentric measures the angle from the center of the earth, not the surface. The almanacs give the angles from the center of the earth. Does not matter for stars but for close-in bodies, primarly the Moon, the angle will be different measured from your position on the surface. This difference is called parallax.

    Hope this helps.

    John H. 41N  100W

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