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    Re: Appeal to forum members to collect data
    From: Frank Reed
    Date: 2007 Oct 27, 22:28 -0400

    Henry H, you wrote:
    "at very least it is rounded off to tenths which in itself leads to possible
    comparitive errors."
    
    The calculator on my web site gives the error in the observation rounded to
    tenths of a minute of arc, e.g. 0.3, but the underlying calculation is as
    exact as possible (almanac data accurate to 1"). The calculator also
    provides the approximate equivalent error in longitude. This listed
    "longitude error" is nothing more than 30x the error in the observation (so
    it's really only the approximate longitude error). But number that gives you
    access to an extra 1.5 decimal places in the result if you really need it.
    In fact, if you take the numerical value for that error in longitude and
    double it, you get the error in the observation expressed in seconds of arc.
    As a specific example, I have a case that says "error in lunar: 0.4'" and
    "error in longitude: 0d 12.8'". Doubling that 12.8 yields 25.6 seconds of
    arc, which should be correct to the nearest second or two.
    
    Note that the mountains and valleys of the Moon's limb introduce variations
    in the Moon's semi-diameter on the order of 2 or 3 seconds of arc. These are
    not taken into account in any lunar distance calculator that I am aware of
    (though it's certainly possible in modern software and eclipse predictions
    generally use the actual limb profile).
    
     -FER
    
    
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