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    Re: Advancing and retiring LOP's
    From: Rodney Myrvaagnes
    Date: 2000 Aug 03, 10:16 EDT

    This is more a problem in error prediction than absolute
    time. If your track passed through an area of circulating
    tide, such as happens in the Gulf of Maine, the DR error
    could be significant in less than 12 hours. But, it might
    cancel out over a longer period. If you are beating to
    weather, your DR is problematic because your VMG varies
    with wave action and wind speed.
    If you can estimate the error range for each of your
    inputs, you could do the calculations for the outer edges
    and get an idea of your final range of error.
    I would advance a two-day-old sun sight if that was all I
    had, but I would be duly sceptical about it.
    On Thu, 3 Aug 2000 09:03:36 -0400, Richard B. Emerson
    >I want to ask a question that was posed by this incident: while
    >acknowledging that there is dilution of accuracy in advancing (or
    >retiring) LOP's as they age (that is, the older an LOP is, the less
    >confidence a navigator should have in advancing that LOP down a DR
    >track), it's been my impression that any LOP within the current
    >navigation day (i.e., noon to noon) is fair game for advancing or
    >retiring.  This implies that, with the understanding of loss of
    >accuracy with time, LOP's as much as 23 hours 59 minutes old can still
    >be used and that LOP's over 12 hours old are certainly still usable.
    Rodney Myrvaagnes                   J36 Gjoa
    Senior Editor           Electronic Products
    etaoin shrdlu

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