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    Re: accuracy of sights and averaging
    From: Peter Fogg
    Date: 2010 Dec 6, 19:13 +1100

    Frank Reed wrote:

    Various people have been advocating plotting a line with the known slope, the rate of increase of the object's altitude

    Or rate of decrease.

      You can calculate this sloping line either by using a unique equation (not complicated, but you have to dig it up and remember it every time) OR, NEARLY AS EASY, and generally more accurate,

    Why more accurate?

    you can just calculate the Hc at some convenient time near the beginning of your set of sights and then calculate Hc again for a time near the end of the set of sights.

    Using a system like this to detect and remove "outliers" (bad sights) is a tougher call, but definitely viable, as Peter Fogg has said, if the outliers are really far out of line. You can't just pare away any and all sights that are inconsistent with a nice line. You need to use a careful and rigorously applied system for removing bad sights,

    And what might such a "system" comprise?

    and in many cases, it's better to keep all the sights since the appearance of an "outlier" may be an illusion, a random accident.

    It may not be an outlier at all.  Once the data is checked, it could turn out to be an altitude or time incorrectly recorded.  This is another advantage of the technique; identifying such problems before these apparent outliers have the chance to pollute the averaged value, which appears to be the alternative.  I have had this happen, particularly when using an assistant to record the sights (not that I'm not error-prone myself!).  Concentrating on the seconds, its all too easy to record the wrong minute of time, etc.

    That's why any such removal system has to be decided on in advance and applied according to the rule without exception.

    What does a "removal system" mean?  Which rule?

       
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