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    Re: Index Error
    From: Robert Eno
    Date: 2004 May 5, 09:57 +0100

    Good point but this was taken into account. For example, yesterday, I
    came home for lunch and couldn't resist taking a quick noon sun shot.
    Index error calculations were as follows:
    32.'0 on  30.'6 off
    Difference = 1.4
    1.4/2 = 0.7
    IC = -0.7
    Now let's take the next confirmatory step:
     32.'0 on + 30.'6 off = 62.6
     62.6 - 0.7 = 61.9
    61.9/4 = 15.5 (rounded up)
    Actual semi diameter = 15.9
    add'l error = 0.4'
    In calculating my noon latitude, I used an IC of -0.7', ignoring the
    other mystery error. My noon latitude differed from actual by 0.1'.
    Pretty close and one could say: "fluke", but I have been getting this
    kind of consistent accuracy with my sextant.
    So the question is, where in the hell does this "other" error come from
    and if I wanted to factor it in to my IC, how do I go about doing this?
    Theoretically, the sum of my off and on readings should have been 63.6
    but I got 62.6.  I should know all of this by now but even someone with
    experience needs to go back to the fundamentals every once in a while.
    I am baffled.  Additional comments welcome.
    >According to the 2004 nautical almanac the semi-diameter of the sun
    varies between 16.3' at perihelion to 15.8' at aphelion. Or the diameter
    varies between 31.6' and 32.6', for a difference of 1.0' or 2 X 0.5'
    >Could this be the source of the error?
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