The tension scale is graduated in pounds from
0 to 30. It is clipped to the eye at the end of the
tape, and the tension is applied until the desired
reading appears on the scale. A pair of staffs can
be used’ to make the work easier. The rawhide
thongs are wrapped around the staff at a
convenient height and gripped firmly. The bottom
end of the staff is braced against the foot (fig.
11-45) and the upper end tucked under the arm.
Tension is applied by using the shoulder and
leaning against the poles. The spring balance is
used in a similar fashion for work of higher
precision.
The stool device in figure 11-45 is called a
tapping stool or chaining buck and is used in high-
precision work. It is a metal three-legged stand
with an adjustable sliding head and a handwheel-
operated device for locking the plate (the top
surface of the sliding head) in any desired
position. A line is scribed on the plate. During
taping operations, the head is moved until
the scribed line is directly under a particular
graduation on the tape; the handwheel is then used
to lock the head. When the tape is shifted ahead
to measure the next interval, the graduation is held
exactly over the line until the next stool is adjusted
and locked. The basic purpose of taping stools
is to furnish stable, elevated surfaces on which
taped distances can be marked accurately. When
stools are not available, 2 by 4s or 4 by 4s are often
driven into the ground for use as chaining bucks.
The length of a tape varies with the tempera-
ture, and the precision of a survey may require
the application of corrections for this. For work
of ordinary precision, you can assume that the
Figure 11-45.-Applying tension to tape.
Figure 11-46.-Tape thermometer.
temperature of the tape is about the same as that
of the air. For work requiring higher precision,
a tape thermometer, like the one shown in figure
11-46, is attached to the tape. For very precise
work, two thermometers, one positioned at each
end, may be used. If the two indicate different
temperatures, the mean between them is cal-
culated and used.
Chaining Pin
A chaining pin (also called a taping arrow) is
a metal pin about 1 ft long. It has a circular eye
at one end and a point for pushing it into the
ground at the other (fig. 11-47). These pins come
in sets of 11 pins, carried on a wire ring passed
through the eyes in the pins or in a sheath called
a quiver.
Chaining pins can be used for the temporary
marking of points in a great variety of situations,
but they are used most frequently to keep count
of tape increments in the chaining of long
distances.
Leveling Rod, Target, and Rod Level
A leveling rod, in essence, is a tape supported
vertically and is used to measure the vertical
distance (difference in elevation) between a line
Figure 11-47.-Taping arrows or chaining pins.
11-42
