ARMY TM 5-6675-308-34
MARINE CORPS TM 08837A-34/2
(1) Grasp the carrying strap with both hands just
(5)
Return the instmment to the first position ((3)
above the two clamping levers and pull out-
above) and again center the bubble.
ward to release the clamping levers from the
Return the instrument to the second position
(6)
base assembly.
((4) above) and again center the bubble.
(2)
Lift the dome-shaped cover directly off the
(7) Repeat (5) and (6) above until the bubble
instrument and lay it to one side,
remains centered in both positions,
(3)
Release the three clamps which secure the
(8) Rotate the instrument 3,200 roils from the first
theodolite to the case base. Grasp the theodo-
position. If the bubble remains centered in this
lite by the standard that has the trademark
position, rotate the instrument 3,200 roils
inscribed on it and lift the theodolite off the
from the second position. If the bubble re-
base.
mains centered in this position, rotate the
instrument throughout 6,400 roils. The bubble
(4)
Attach the instrument to the tripod head by
should remain centered; if it does, the instru-
screwing the fixing screw snugly into the base
ment is level.
of the tribrach.
(9) If the bubble is not centered when the instru-
(5) Replace the cover on the base of the case to
ment is rotated 3,200 roils from the first posi-
prevent dust and moisture from entering the
tion ((8) above), the level vial is out of adjust-
case.
ment. To compensate, move the bubble half-
way back to the center of the level vial, using
the same leveling screws that were used for
ocedure. for plumbing and leveling the theodolite is as
the first position. Rotate the instrument 3,200
follows:
roils from the second position and move the
(1)
Loosen the fixing screw slightly and carefully
bubble halfway back to the center of the level
move the instrument around on the head of
vial, using the one remaining leveling screw.
the tripod until the point of the plumb bob is
The instrument is now level, and the bubble
centered exactly over the station.
will come to rest in its vial at the same off-
center position regardless of the direction in
Tighten the instrument to the tripod head,
which the instrument is pointed. The level vial
making sure that the point of the plumb bob
should be adjusted at the first opportunity.
remains centered over the station.
(10) After the instrument is leveled, check the
optical plumb to ensure that the instrument is
centered exactly over the station. If it is not,
center the instrument over the station by shift-
ing it on the tripod head, and again check the
Excessive tightening of the fixing screw
level of the instrument. If necessary, repeat
will bend the slotted arm and damage the
the leveling process and again check the opti-
tripod head.
cal plumb. Repeat this process until the instru-
Loosen the leveling screws to expose sufficient
(3)
ment is level and centered over the station,
thread (3/8 to 1/2 inch) on the three screws to
d. Focusing the Telescope to Eliminate Parallax.
permit the instrument to be leveled. Rotate
Before a theodolite is used for measuring angles, the
the instrument until the axis of the tubular
telescope must be focused to eliminate parallax by
level is parallel to any two of the three level-
bringing the focus of the eyepiece and the focus of the
ing screws. Center the bubble by using these
objective lens to the plane of the reticle (crosslines).
two leveling screws. Grasp the leveling screws
This is accomplished as follows: Point the telescope
between the thumb and forefinger of each
toward the sky or a neutral background and rotate the
hand and turn the screws simultaneously so
knurled ring on the telescope eyepiece until the reticle
that the thumbs of both hands move either
crosslines are sharp, distinct lines. (In doing this, the
toward each other or away from each other at
observer should be very careful to focus his eye on the
the same time. This movement tightens one
crosslines, not the sky). Next, point the telescope
screw as it loosens the other. The bubble
toward a well-defined distant point and, still focusing
always moves in the same direction as the left
the eye on the crosslines, bring the point into a clear,
thumb.
sharp image by rotating the knurled focusing ring on
the telescope. Use the horizontal tangent screw to
(4) Rotate the instrument 1,600 roils; this places
one end of the plate level over the third
center the vertical crossline on the point. To check for
leveling screw. Using this screw, center the
elimination of parallax, move the eye horizontally back
bubble,
and forth across the eyepiece. If the parallax has been
5-6
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