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(Turn another 90" and check bubble position)
8) Turn the upper part of the instru-
ment a further 90" and check to
see if the bubble is in the centre of
the plate level
Q.
If the bubble is off-centre, per-
form the following:
@
Adjust levelling screws A and
B i n equal and opposite direc-
B
tions, t o remove half of the
bubble displacement.
O
Turn the upper part a further
90°, and use levelling screw C
t o remove half of the dis-
placement in this direction.
Or try the adjustment described
on P.177, under "23.1 Plate level".
Check to see if bubble is in same position in any direction
9) Turn the instrument and check t o
see if the air bubble is i n the same
position for any position of the
upper part.
If
it
is not, repeat the levelling
procedure.
Focus on the centre of the reticle again
10) Loosen t h e c e n t r i n g s c r e w
@
slightly.
11) Looking t h r o u g h t h e optical
+
plummet eyepiece, slide the in-
@
strument over the tripod head
until the surveying point is ex-
actly centred in the reticle.
12) Re-tighten the centring screw se-
curely.
(check plate level bubble again
)
13) Check again to make sure the
b u b b l e i n t h e plate level i s
centred. (If not, repeat the proce-
.
dures starting from step 4.)
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