Figure 17-20. Or use parallel (of latitude) as reference. Figure 17-21. Reading a course line
3. Rotate the plotter using pencil point as
a pivot until the desired course on the
plotter scale aligns with the meridian
or parallel (Figure 17-19b). Double
check to make sure bulls-eye is still on
the same meridian or parallel. Draw the
course line (Figures 17-19b & 17-20)
Reading a Course Line
Align the course line with any of the plotter
lines (Figure 17-21).
Which Scale to Use
When using a meridian of longitude, read
the outer two scales; this generally works
better for courses running more east or west.
When using a parallel of latitude, read
the inner two scales; this generally works better
for courses running more north or south.
There are two sets of numbers on both
the inner and outer scales; they are reciprocal
courses depending on which way you
are going. Use the test of reasonableness:
Consider which direction your course
is going and make sure you read the number
corresponding to the proper one of
these four quadrants (Figure 17-22).
Label the course parallel to and
directly above the course line and near the
point of departure. The course direction
should be written using three digits preceded
by the letter C (for example, C070).
Figure 17-23 shows how to label a course
line.
Section 17: Introduction to Navigation 201
Note:
• Usually, the direction of the course line
and its location on the chart will dictate
whether it is easier to use a horizontal or
vertical grid line.
• Remember, when you measure distance
as described in the next section, you can
use the latitude scale—but NEVER use
the longitude scale.
• Course direction is labeled above the
course line as three digits following a “C”
for “course” close to the start of the course,
and distance is labeled below the line near
its mid-point to one decimal point follow-
84
85
86
87
88
89
90
91
Figure 17-22. Direction of course