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    Re: Averaging
    From: Gary LaPook
    Date: 2004 Oct 20, 15:16 -0700

    Not to be too "nit picky" but it should be a plot of a "small circle,"
    not a "great circle." A straight line is a good approximation of the
    small circle at lower latitudes and short intercepts. At high latitudes
    you should use the "Ellsworth Tables" to calculate how much the small
    circle diverges from the simple straight line and plot a modified LOP
    which is then more accurate.
    As long as we are talking about the St. Hilaire method (computing an
    azimuth and intercept from an assumed position) we should remember that
    it was developed as an easy method of laying down the "Sumner Line," now
    called an  LOP,  requiring only one computation. The original Sumner
    method required computing two time sights, twice as much work. With
    programmable calculators it is now just as easy to do the two
    computations and lay down the LOP without measuring an azimuth or
    intercept  or using an assumed position. You  simply choose two
    longitudes, one east and one west of your DR, and the calculator
    calculates the latitude where the LOP crosses those longitudes. You
    prick those latitudes on the chart and draw a straight line between them.
    Gary LaPook
    Chuck Taylor wrote:
    >Standard procedure for plotting a line of position
    >using the St. Hilaire method calls for plotting a
    >straight line, when we know that what we "should" be
    >plotting is the arc of a great circle.  Still, the
    >straight line is useful.
    >Chuck Taylor
    > 47d 55' N
    >122d 11' W
    >Do you Yahoo!?
    >Yahoo! Mail - You care about security. So do we.

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