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    Re: Wires, back sights and collimation
    From: Alexandre Eremenko
    Date: 2004 Dec 1, 00:28 -0500

    Frank,
    
    On Tue, 30 Nov 2004, Frank Reed wrote:
    
    > As long as contact is made with some portion of the Moon's
    > disk crossing the centerline of the field of view
    > (which is easy and normal
    > in  practice and implies that i is less than 16 minutes of arc),
    
    I do not find this easy with distances more than 90,
    and sextant in awkward position. Maybe because I have not practiced
    enough.
    And this is exactly where I think the wires are helpful.
    
    The second use of wires is checking the collimation itself.
    Of course, on most modern sextants, collimation is not adjustable,
    so there are no reasons to check it.
    
    The third use of wires (according to Maskelyne) is checking that
    your sextant is perpendiculat to the horizon, especially when taking
    altitudes close to 90. This I had no opportunity to test yet.
    
    Alex.
    
    
    

       
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