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    Plotting in Magnetic vs True
    From: Lu Abel
    Date: 2009 Aug 04, 16:31 -0700

    My just-posted question on DR plotting actually arose while researching
    a different topic:
    When did plotting courses in True (vs Magnetic) become  commonplace?  In
    fact, were courses in a plot originally labeled in True or Magnetic?
    I suspect that with the advent of the gyrocompass on ships knowing True
    courses became important.  But there were centuries and centuries of
    navigation before the perfection of the gyrocompass that depended on
    magnetic compasses and it might have made a lot more sense to plot in
    Of course, if navigators didn't keep a DR plot then the whole True vs
    Magnetic issue becomes more difficult to answer.
    The only reference I've found to True vs Magnetic is in browsing through
    NOAA's on-line library of antique charts.  A very few of them have
    courses between prominent objects which are labeled in Magnetic using
    the traditional intercardinal point notation.  An excellent example of
    this is a chart of Woods Hole (although the chart calls itself Woods
    Holl, search for chart 348), a marginal note says "directions not shown
    in brackets are Magnetic, those in brackets are True"   All directions
    are unbracketed.
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