Figure 4.2-18 Measuring East/West Direction
CAUTION: Be careful to interpret the scales of the plotter correctly. Always look at the
scale numbers to both the left and the right of the meridian being used. This is known as
bracketing and eliminates erroneous answers that could be off by as much as ten degrees.
If a course line runs generally north and south, it may be difficult, if not impossible, to slide
the plotter along the course line until a meridian falls under the plotter's grommet. The
north/south scale (the innermost scale on the plotter) can be used in this situation.
The procedures are the same in that the plotter's straight edge is kept on the course line,
but now a parallel is placed under the plotter's grommet. Then, follow that parallel out to
the inner north/south scale to read the answer (Figure 4.2-19). Again, there is a choice of
two answers, so it is imperative to estimate the general course direction before beginning.