If the ground slope is fairly uniform, and if
the tape corrections do not exceed 1 ft, a plus
100-ft tape is very useful to establish these station
points. The head chainman determines the slope
correction first, then lays off the true slope
distance that gives a horizontal distance of 100
ft. If the slope is less than 2 percent, no slope
correction is required. Slope corrections will be
discussed later in this chapter.
Horizontal Chaining
In horizontal chaining, the tape is supported
only at its ends and held in a horizontal
position. Plumb bobs are used to project the end
graduations of the tape (or, for a less-than-tape-
length measurement, an end and an intermediate
graduation) to the ground. Be very careful when
you use the plumb bob both in exerting a steady
pull on the tape and in determining when the tape
is horizontal.
PLUMBING.— Plumbing is complete when
the tape is in horizontal alignment and under the
proper tension.
The rear chainman holds a plumb bob cord
at the proper graduation of the tape, and the point
of the plumb bob about one-eighth of an inch
above the marker from which the measurement
is being made. When the plumb bob is directly
over the marker, he calls, “Mark!”
The head chainman holds a plumb bob cord
at the correct graduation of the tape with the point
of the plumb bob about 1 in. above the ground.
He allows his plumb bob to come to rest; sees that
the tape is horizontal; checks its alignment and
tension; and when the rear chainman calls,
“Mark!” allows the plumb bob to fall and stick
in the ground. This spot is then marked with a
chaining pin.
At times, in rough country, a small area
around the point may require clearing for
dropping the plumb bob. Because the clearing is
usually done by kicking away small growth, this
type of clearing is commonly called a KICKOUT.
To determine the approximate location of the
kickout, the head chainman may call, “Line for
kickout!” and then “Distance for kickout!” At
“Line for kickout!” the rear chainman or
instrumentman gives the approximate line by
eyeball. At “Distance for kickout!” the rear
chainman holds approximately over the starting
point without
plumbing.
LEVELING
shows a pair of
being too particular about
THE TAPE.— Figure 12-13
chainmen making a horizontal
measurement on a slope. You can see that, to
make the tape level, the person at the lower level
is holding the end at chest level while the person
at the higher level is holding it at knee level.
To maintain the tape in a horizontal position,
the chainman at the lower level held the hand
level. By studying the position of the other
chainman, he decided that it would be possible
to hold the tape at chest level. He then held the
hand level at about the height of his own chest
level and trained it on the other chainman. It
indicated that a level line from his own chest level
intersected the person of the other chainman at
that person’s knee level. So he called out, “At
Figure 12-13.-Horiziontal chaining using plumb bobs.
12-14
