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    Re: Full moon sights and lifeboat sextant accuracy
    From: Greg Rudzinski
    Date: 2017 Oct 6, 17:53 -0700


    The liquid artificial horizon cuts the systematic errors in half so that the actual natural horizon intercepts due to systematic errors are going to be double that observed in the artificial horizon. I have three metal sextants (Tamaya Jupiter, C&P, and US Navy M,Low) that will all be at 1' intercepts or better using a x4 scope on the liquid artificial horizon. Making observations on a natural horizon from a sailboat cockpit will be a different story. 3' intercepts would then be concidered good if using a metal sextant.

    Greg Rudzinski

    PS I'll do a set of 10 observations each for you tomorrow. C&P with x4 scope vs. Davis MK 3 with sight tube (using a liquid artificial horizon).

    I'd like to see results from a set of runs, one with the MK3 another with
    a "good" sextant under the same conditions.  These results do not seem too
    bad to me.  Certainly good enough to put on a reasonable sized island.
    > Jing,
    > The Davis MK 3  accuracy is in the + or - 8' range out of the box. Better
    > results are possible but you have to earn it. Plastic sextants will warp
    > in direct sun light or if squeezed too hard. I zero the index error before
    > each observation then check again after the observation. Even if
    > everything is done right there will remain large systematic errors. Below
    > is a set of 5 observations using a Davis MK 3 and a liquid artificial
    > horizon today. Good enough in a pinch but not very good as a primary
    > sextant.
    > Intercepts:
    > 3.7' toward
    > 2.0' toward
    > 2.8' toward
    > 3.0' toward
    > 1.4' toward
    > The MK 3 is very good for horizontal sextant angles, and relative bearings
    > off the bow. Sailboat racers can use to see if gaining or losing on a
    > competitor.
    > Greg Rudzinski
    > [plain text auto-generated]
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