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    Re: Practice Bubble vs. Professional Bubble
    From: Ken Gebhart
    Date: 2012 Aug 5, 21:13 -0500

    I feel I should say a few words, since it is our product.
    1.  It is my belief that part of the inaccuracy experienced with the
    PBH is the slit which allows focus on a star and the bubble
    simultaneously. I think that if you move your eye slightly, you will
    actually see a different picture of the bubble. Perhaps a different
    retinal image.  I am thinking of the eye test where you state which
    stair step the line passes through. I you blink, you will get a
    different answer.  Perhaps some eye expert will comment on this, and
    correct me if I am wrong.
    2.  I have personally taken star sights during star time (when there
    is enough ambient light to  see the bubble, but sufficiently dim to
    see a bright star) in Kansas where there is low light pollution.
    3.  We call it a "Practice" bubble horizon because of the inherent
    inaccuracies.  Just to give a beginner some numbers to crunch.
    4.  It's one of the few products we "push", because it lets
    landlocked people use their sextants more often.
    On Aug 5, 2012, at 5:30 PM, bill wrote:
    > On 8/5/2012 6:17 PM, Alan S wrote:
    >> I have tried the practice bubble horizon without successa,
    >> possibly my
    >> fault, the thing seems "tricky" to use and I have yet to get an
    >> understandable explaination of the bubble correction factor, as
    >> with how
    >> to determine it, ....
    > It is simply a matter of looking at the difference of Ho and Hc
    > from a known position (plus/minus IE).
    > Under the K.I.S.S. principle, I determine LAN for my location, and
    > do several observations while the sun's elevation changes very
    > little. I also preset for Hs.
    > In an attempt to minimize centering the bubble errors while
    > aligning the sun, I had tripod mounted my preset sextant with the
    > bubble as close to centered as I could see it. Even then results
    > were plus/minus 2', so accurately seeing bubble placement is a
    > limiting factor.
    > Bill B

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