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object where the observer sees the cross hairs apparently located. Thus the cross
hairs and the optical center of the objective define the line of sight of a telescopic
sight.
b. The Spirit Bubble Tube Or Circle
A spirit bubble vial consists of a glass container, which is partly filled with a
clear, nonfreezing, very low viscosity liquid such as alcohol or ether.
Level Rods
There are many different types of level rods. Generally, the body of the rod is
made of seasoned hardwood; this act as a rigid support for the rod face, a strip of
steel graduated upward starting from zero at the bottom. The rod person, on a point
of known elevation for a BS, or a point of unknown elevation, holds the rod
vertically for an FS. The rod is then observed with the level and read by the
instrument person on the target rod.

Fig. 5.6 Traditional rectangular cross-section leveling rods
showing a variety of graduation markings

Fig 5.7 Circular rod level

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