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    Re: Artificial horizon question
    From: Peter Hakel
    Date: 2009 Apr 20, 14:16 -0700
    John,

    There is no dip correction for the height of eye in this case.  The index correction always needs to be made.  If you overlap the disks then there would be no semidiameter correction either.  However, I believe that more frequently than not people bring the disks to touch each other, in which you do have to correct for the semidiameter after you divide the (index corrected) sextant altitude by 2.


    Peter


    From: "JKP{at}obec.com" <JKP{at}obec.com>
    To: NavList@fer3.com
    Sent: Monday, April 20, 2009 12:51:57 PM
    Subject: [NavList 8001] Re: Artificial horizon question


    Brad,
    Tnhnaks for your advice.  I'll see if I can check the parallelism as you describe.

    GTeorge, Thanks for your advice as well.  I will either get a piece of black glass (and devise a means of leveling it as I have read in past posteings) or at least try some sort of non-reflective treatment for the pan bottom.

    I don't particularly suspect that I'm getting a double image from the oil pan, however.  When sighting the sun, I use a colored cover over the artificial horizon pan, and different colored filters between my eye and the sun, and I get two distinctly colored images, say green from the sky and yellow from the pan.  It is these that can't seem to be brought very near each other horizonatally.  That is, until for one luck second they slip right over one another, and if I'm quick with the micrometer I can get my shot beforfe they agaion wobble apart.

    By the way, I had also meant to ask:  Should I ignore altitude correction when using an artificial horizon?  Clearly no correction for semi-diameter should be needed, because I am superimposing full discs of the sun and its reflection, center-over-center, rather than touching the upper or lower limb to the horizon.  But I guess I can't grasp the principle behind altitude correction sufficiently to decide whether it counts in this situation.

    -John



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