does not require patrol members to
leave
the
roadway.
It
can
be
accomplished on any kind of terrain.
(2) Tape Method.
This method is particularly suited for
measuring very sharp curves on relatively level ground.
First, you
establish points at each end of the curve, along the centerline. These are
called the point of tangency (PT) and the point of curvature (PC).
See
Figure 1-18.
One individual stands at the estimated center of the circle
and holds one end of a pate measure. A second person walks the arc of the
circle from PC to PT. They adjust the length of the tape so that it is the
same distance from the center to PT as to PC. That distance is the radius
of the curve.
(3) Triangle Method. The approximate radius of a curve may be
determined by laying out 3:4:5 ratio right triangles.
This method may be
used when obstructions preclude walking the curve, as is done in the tape
method. As with the tape method, first determine PC and PT. Then lay out
right triangles as illustrated in Figure 1-19.
You then extend the base
legs of each triangle until they cross. The distance from where they cross
to either PC or PT is the approximate radius of the curve.
f.
Steep Grades.
Grades of 7 percent or more are considered steep grades.
For
route reconnaissance purposes, they are considered an obstacle (OB).
A7
percent grade is one that rises at a ratio of 7 in 100. For example, if,
after traveling 100 feet, the road is 7 feet higher than when you started,
it is a 7 percent slope. Any slope of 7 percent or more must be noted on
your overlay. There are four symbols on an overlay for steep slopes. All
slopes are indicated by an arrow. The arrow points in an uphill direction.
If the scale of the map permits, the arrow should be the length of the
slope. To the right of the arrow you show the actual percent of slope. A
slope of 5-7 percent has a single arrowhead; from 7-10 percent, there are
two arrowheads; from 10-14 percent, three; and over 14 percent has four.
There are several methods for calculating the percent of slope.
Which one you use depends on the time and equipment you have available.
There is an instrument called a clinometer that engineer units have that
will measure the slope directly. These are not normally found in MP units.
When you organize your patrol, you might consider borrowing one from an
engineer unit, if possible.
1-47
MP1028
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