Page 89 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

SURVEYS AND MEASUREMENTS 2.39

FIGURE 2.36A Hand level.

shoe rests on the ground at eye level. The spot is marked, the observer moves to it, standing with
his or her heel on it, and the rod operator moves uphill, repeating the process. When the top is
reached, the last observation should be taken on the rod, or a ruler or tape, to show the distance
from the hilltop up to eye level. The height of the hill is the height of the observer, multiplied by
the number of observations, less the rod reading on the last observation.
In working downhill, Fig. 2.36(B), a target fastened at the top of the rod, or a mark on a long
stick, is sighted and moved until it is level with the eye. The observer then moves to that spot,
while the target is moved downhill until level with the new position. On the last sight, the distance
from the ground to eye level is measured.
Each observation covers a drop equal to the height of the target minus the height of the observer, and
they will all be equal except the last one, which should be separately figured and added to the others.
An individual’s eye height, measured from the heel when she or he is in erect position, will
seldom vary more than an inch, which is not too large an error for rough work. Care should be
taken that the heel, and not the ball of the foot, is placed on the mark.
Level Clinometer. The clinometer is a special type of hand level which can be used to measure
slopes and vertical angles. The spirit level is hinged so that it can be rotated about 45° in either
direction, and a pointer and scale indicate the angle between the spirit level and the line of sight.
The bubble will appear at the centerline of the object glass when the hand level is held at the angle
indicated by the scale. The scale is usually graduated to indicate both angles and slopes.
The angle of a slope may be measured by setting a target at eye height at one end and sighting
it from the other. With the centerline on the target, the spirit level may be adjusted until the bub-
ble is beside the line. The pointer on the scale will then indicate the slope of the hill.