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4. Centering
“Centering” refers to the precise alignment of the instrument’s central axis
over the station point. This can be accomplished in two ways, through
the use of a plumb bob, or the optical plummet.
1) Using Plumb Bob
For the models with detachable leveling base
(1) Place the instrument on the tripod head. Insert the instrument clamp
screw into the center hole of the instrument’s base plate and tighten.
(2) Hang the plumb line on the hook of the instrument clamp screw.
Adjust the length of the plumb line so that the tip of the plumb bob is
approximately level with the station point.
(3) Slightly loosen the instrument clamp screw. Supporting the outer
side of the leveling base with both hands, carefully slide the
instrument on the tripod head until the tip of the plumb bob coincides
with the center of the station point.
•
Confirm precise alignment by viewing from two directions at right angles to
each other.
