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Compass Error Calculations
Background
In navigational work, you have to develop the ability to quickly and
accurately convert directions between true, magnetic, and compass
(headings, courses, and bearings).
A heading or course is the same as an angle. It is the angle that the
centerline of the ship or boat, or a line marked on a chart makes with
some other reference line.
Reference
Three lines of reference have been established: the direction of true
north, or the true meridian; the direction of magnetic meridian; and the
direction of the north point of the compass. Ship’s heading is the same.
How you describe it depends on the reference point used.
There are three ways to
name a course or
heading:
True heading
Magnetic heading
Compass heading
Comment
Whether you are determining courses the helmsman is to steer, obtaining
bearings to be plotted on a chart, laying track lines on the chart, or
recording courses in the Magnetic Compass Record Book, knowing how
to apply variation and deviation comes into play. The big question is
"how do we convert one to the other?" Practice is needed to perform
this task. However, keep in mind that you first need to reason each
step, until later when the process becomes habit.
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