Figure 11-43.-Types of tape clamp handles.
marked circle reticle adjusted to be in line with
the vertical axis of the instrument. After the
instrument is leveled, a sighting through the
plummet will check the centering over a point
quickly. The advantages of the plummet over the
plumb bob are that it permits the observer to
center over a point from the height of the
instrument stand, and it is not affected by the
wind. The plummet is especially useful for work
on high stands. A plumb bob requires someone
at ground level to steady it and to inform
the observer on the platform how to move the
instrument and when it is exactly over the point.
With the plummet, the centering and checking is
done by the observer.
Tape Accessories
There is usually a leather thong at each end
of a tape, by which the tape can be held when the
full length is being used. When only part of the
tape is used, the zero end can be held by the thong,
and the tape can be held at an intermediate point
by means of a tape clamp handle, like those shown
in figure 11-43.
When a tape is not supported throughout—
that is, when it is held aboveground between a
couple of crew members—a correction must be
applied for the amount of sag in the tape. To
make this correction, you apply a certain amount
of tension. Figure 11-44 shows two devices for
applying a given amount of tension.
45.780
Figure 11-44.-Tension scale and spring balance.
11-41
