Geoscience Reference
In-Depth Information
Fig. 2.7 Principle of
leveling
Fig. 2.8 Structure of the
level
1. The line of sight is parallel to the axis of the bubble (level) tube.
2. The axis of the level tube is perpendicular to the vertical axis.
In this case, when the instrument is leveled with the bubble tube, the line of sight
will be horizontal in all directions.
Precision dictates whether the leveling instrument can be classified as a precise
leveling instrument or an ordinary leveling instrument. A precise leveling instru-
ment is chiefly used in high-precision height measurement as in national first- and
second-order leveling and precise engineering surveying. An ordinary leveling
instrument is used in general engineering construction and topographic surveys.
The major difference between these two types is that the precise leveling instrument
has a built-in optical micrometer for accurate readings.
The leveling rod is an important leveling instrument that can be used to deter-
mine the difference in height between points.
A precise leveling rod has a 26 mm-wide and 1 mm-thick Invar strip placed in
the grooves of the wooden part of the rod, with one end fixed to the base plate and
the other to the metal frame at the top of the rod by a spring. Graduations of the rod
are painted to fill the grooves cut in a scribed rule and the graduation lines are
painted on the wooden part of the rod. The rod is approximately 3.1 m in total
length.
The rod can be graduated at intervals of 10 mm or 5 mm, according to the
measurement range of the level micrometer. Graduations are painted in two col-
umns on the left and right sides of the rod.
The rod holder loop is also configured to both the back sides of the leveling rod
to help hold it. The rod stand or stake is installed to keep the rod steady and upright.
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