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    Re: Children's land-locked "Sextant"
    From: Bill B
    Date: 2007 Nov 28, 02:57 -0500

    > The Davis Mark 3 sextant runs about $35 and would be good for a group
    > of kids to get their hands on. Since there are no optics, it is pretty
    > easy to line up the suns image using an artifical horizon.
    >
    > I blieeve Omar Reis on his web site shows how to make a sextant out of
    > a CD.
    
    I am familiar with Omar's CD sextant. Celestaire offered a "build it
    yourself" cardboard sextant and optional bubble horizon at a very attractive
    price. (By all means splurge for the bubble if landlocked.) If assembled and
    used carefully, this unit(s) will provide consistent results that are better
    than advertised.  I am good to plus/minus 3 minutes of an arc with it
    (including using the optional bubble horizon) on a regular basis.
    
    For the anal retentives:
    
    Upsides
    --Inexpensive.
    --Very useable bubble horizon, can be lighted easily from above.
    --Vernier scale easy to interpolate.
    --All but index error adjustable on the spot by bending
      the cardboard a bit.
    
    Downsides
    --Requires care in assembly.
    --No horizon filter(s).
    --Not suitable for a wet marine environment.
    --Front silvered mirrors (actually polished stainless
      steel if I read it correctly--are identical in size.
    NOTE:  This eliminates the need for glass on the see-through side of the
    traditional horizon mirror as there is no refraction to cope with. However,
    due to distance (index mirror smaller via perspective) there is a gap that
    makes aligning stars or the horizon a pain in the a_s without bending the
    cardboard frame and introducing other errors. As a designer--or if I were to
    build another--I would adjust sizes or shim one so I had an uninterrupted
    view between the horizon and index mirrors.
    
    Bill
    
    
    
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