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    Re: Practice Bubble Horizon
    From: Bill B
    Date: 2014 Feb 27, 17:14 -0500

    On 2/27/2014 2:41 PM, Sean C wrote:
    > I'm close to being able to buy my first metal sextant. I will most
    > likely get the Astra IIIb. I was just wondering if anyone has used the
    > "practice bubble horizon" sold by Celestaire and others. If so, what did
    > you think of it? Is it worth purchasing? Thanks in advance for any advice.
    
    I found it worthwhile. Like almost anything Celestaire sells it performs
    as well or better than advertised. If I recall the last time I reviewed
    it Ken thought I was being unkind. That was not my intention, but rather
    to point out its strengths and weaknesses from my vantage point.
    
    For the price, it is hard to beat (with the exception of an artificial
    horizon). The experience somewhat like being on the water on a choppy
    day. To paraphrase one reviewer, "It's like trying to take a shot while
    balancing atop a beach ball in a swimming pool." For me, it is closer to
    making observations from a light to medium displacement sailing vessel
    with a fin or wing keel in 5' to 7' waves. One has to keep himself or
    herself stable, keep the sextant vertical, keep a body which is moving
    up and down and left and right centered in the scope and in the sweet
    spot of a traditional mirror while bringing the body tangent to the
    horizon, quite possibly with a zero-magnification tube. This all has to
    come together while at the crest of a wave. Doable, but an order of
    magnitude more difficult than an AH or standing near the water's edge.
    
    The largest problem I have is centering the relatively large horizontal
    bubble on the center line while doing the same for a zero mag body.
    Bisecting the sun with a relatively thick line is not too difficult. I
    feel the addition of limiting lines to the reticle would be a huge plus.
    Even if the bubble size changes slightly, bracketing it between two
    lines with a slight overlap or gap would be more precise and accurate
    for me. (Not unlike centering a bubble in a circle on an aircraft
    sextant.) I have had some success placing masking tape on either end of
    the light portal to create a bracket of sorts. The pitfall here I
    suspect may be that the masking tape is not on the reticle or spirit
    level, so it casts a shadow that may change position based on the
    direction of the incoming light. More testing is called for.
    
    I do keep a piece of masking tape on the body, as there are times when
    the alignment of the sun to the light portal creates way to much
    brightness on the bubble. In that event I place the tape over the light
    portal to act like a sextant shade.
    
    Admittedly I have not played with it much since I've been living within
    a 30 minute drive to Indiana's north shore. I plan to take it to Lake
    Michigan once the Midwest deep freeze subsides, and the pack snow and
    shelf ice melt off.  Much easier to obtain an accurate SIC with a
    natural horizon than being landlocked and playing around with LAN
    observations.
    
    Bottom line, I feel it is a good training aid. I do not feel it is
    accurate enough to provide me feedback for fine tuning my skills with a
    metal sextant at this point. That is best done with an AH or natural
    horizon.
    
    You've done very well indeed with your Davis. It is time to reward
    yourself. Drink like a Greek god and purchase a metal sextant. IMHO you
    will be more than pleased with an Astra IIIB should you decided to go
    that way.
    
    Hope that helps
    
    Bill B
    
    

       
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