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    Re: Calibrating a sextant scale
    From: Fred Hebard
    Date: 2007 Nov 20, 12:30 -0500

    Yes, for star-to-star distances, you have to correct for spherical  
    aberration when clearing the observed distance, just like the moon.   
    It's been tried.  The problem is getting a precise star-to-star  
    distances.  I don't believe anybody claims to have solved that  
    problem.  The only solution seems to be to take it to somebody who  
    has a calibrating machine, or roll your own if you have access to  
    tens or hundreds of thousands of dollars of optical equipment.
    On Nov 20, 2007, at 11:01 AM, Isonomia wrote:
    >> Then calibrate for index error as you already know. If any large  
    >> errors
    >> are found and corrected for you should repeat the last two steps.
    >> Nicol�s
    >>  cal_index_mirror.jpg
    >> 49KViewDownload
    > Nicol�s, thanks - I should have said that I had done the basic
    > calibration as you suggested.
    > The real question I was asking is having done the zero calibration,
    > how would I check the error at other readings?
    > ... the answer must be to take readings between two known stars (not
    > risking life an limb off a cliff!) which I presume will be very
    > accurate - but perhaps its not that simple because each will have some
    > refraction through the atmosphere.
    > Has anyone tried this?
    > Mike
    > >
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