and right in the notebook must correspond to left
and right in the field.
Figure 14-20 shows field notes for cross-
section levels taken on the first three stations
shown in figures 14-16 and 14-17. On the data
side, only the station and the HI need to be listed.
On the remarks side, each entry consists of a point
elevation, written over the distance of the point
from the center line. The computed elevation,
determined by subtracting the rod reading from
the HI, is written in above as shown. Note that
the rod reading at the center line is the 5.5-ft
vertical distance from your line of sight to the
ground. Also, notice that the center-line elevation
written in at each station. is the one obtained in
the profile level run. You obtain the HI for each
station by simply adding together these two
figures.
Double Rodding
Double rodding is a form of differential
leveling in which a continuous check is maintained
on the accuracy of the leveling procedure. It is
called double rodding because it can be done most
conveniently by two rodmen. However, it is
possible to carry out the procedure using only one
rodman.
In double rodding, you determine the HI at
each setup point by backlights taken on two
different TPs. If no mistake or large error has
been made, the result will be two HIs that differ
slightly from each other. Elevations computed this
way will also differ slightly. In each case, the
average is taken as the elevation.
Figure 14-21 shows double-rodded level notes
for a run from one BM to another by way of three
Figure 14-21.-Sample field notes from double-rodded levels.
14-20
