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    Re: Index Correction
    From: Alexandre Eremenko
    Date: 2007 May 6, 04:47 -0400

    I am surprised that you can determine a difference
    in IC before and after an observation.
    What sextant are you talking about?
    (I've heard such things about plastic sextants
    but not about metal ones).
    By how much it changes?
    Are you sure that it really changes
    (this can be a random error, rather then change
    due to temperature).
    In my case, IC does not change for months,
    and I could never detect any noticeable dependence
    on the temperature.
    On your statistical question: Of course, I would just
    take the average IC before and after, as you do.
    > It is common practice to check for IC before and after a round of sights.
    > In my experience, they are seldom the same particularly when taking sights
    > under non-standard temperatures.
    > Question: what correction would you apply?  Generally what I do is a
    > combination of fudging and black magic but it usually entails simply
    > taking the two ICs and averaging them to arrive at a single IC that can be
    > applied to the entire round of sights.
    > Please: I am not looking for involved statistical computations. I am
    > trying to determine what other navigators do in the field/at sea.
    > cheers,
    > Robert
    > >
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