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    Re: Navy MK 5 Octant Using Natural Horizon
    From: Greg Rudzinski
    Date: 2012 May 1, 08:39 -0700

    Alex, You stated:

    "I don't see a reason to substitute a normal sextant with a bubble octant
    if the real horizon is available, except that a bubble octant is usually
    cheaper. But the performance of your bubble octant seems to be quite
    exceptional."

    Bubble octants are quite a bit cheaper but buyer beware for these old instruments have seen combat. I got mine four years ago with everything working except for the averager. Getting the averager working was no easy task. Fixing a bubble octant is probably an order of magnitude harder than fixing a traditional sextant. Keep this in mind before tearing into one. If things do go terribly wrong we have Bill Morris to back us up :)

    "(But these are excellent results for a bubble octant!
    I have never heard of the 0.1' accuracy obtained with a bubble octant,
    even if this is an average of 30)"

    Getting good results is more of a matter of having the correct index correction known and applied. The index correction on the bubble octant used for these natural horizon trials is +6' moa and was first determined by lining up the horizon (as normally done with a marine sextant) then double checked by lining up a twilight star. The Sun can't be used to check index error because there are no filter sets for the horizon prism.

    Greg Rudzinski

    [NavList] Re: Navy MK 5 Octant Using Natural Horizon
    From: Alexandre Eremenko
    Date: 1 May 2012 02:15
    Greg,
    Thanks for your explanation.
    I did not realize that this was the bubble octant:-)

    (But these are excellent results for a bubble octant!
    I have never heard of the 0.1' accuracy obtained with a bubble octant,
    even if this is an average of 30)

    > There is no way to get results like I did with a
    > bubble horizon even on my luckiest day ;-)

    I thought tat there is no way to obtain the results you are talking
    about with a bubble octant at all:-)
    But I have never tried my bubble octant with the real
    horizon.

    > I was happy to get near marine sextant performance
    > which means that this particular octant with horizon
    > prism is good enough to substitute for a marine sextant
    > aboard ship or small craft.

    I don't see a reason to substitute a normal sextant with a bubble octant
    if the real horizon is available, except that a bubble octant is usually
    cheaper. But the performance of your bubble octant seems to be quite
    exceptional.

    Alex.

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