Install guide

reverse points is less than 0.05 mil (10”). When
this adjutment is completed, repeat the vertical-
ity test to insure that the vertical crossline is still
perpendicular to the horizontal axis of the tele.
scope.
NOTE
This adjustment can also be made with
the telescope in the reverse position, us-
ing the mean value for the reverse point-
ing, i.e., 3,200.500.
5-19. Vertical Collimation Adjustment.
a.
b.
c.
Purpose. The purpose of the vertical collimation
justrnent is to make the line of sight horizontal
when the vertical circle reads 1,600 mils with
the telescope in the direct position (4,800 mils
with the telescope in the reverse position) and
the ends of the collimation level bubble are in
alignment.
Test. To test the vertical collimation, select a
well-defined point at least 100 meters from the
instrument. With the telescope in the direct
position take a vertical circle reading on the
point, making sure that the collimation level
bubble is precisely aligned. Plunge the telescope
to the reverse position and again take a vertical
circle reading to the same point. The collimation
level bubble must be precisely aligned before,
and checked after, each vertical circle reading.
Repeat these two measurements to insure that no
error was made. The sum of the two readings
should equal 6,400 mils. Assuming no error in
the pointings or readings, any difference between
the sum of the two readings and 6,400 mils is the
apparent (index) error, or twice the collimation
level error. If the difference exceeds plus or
minus 0.150 mil (30”), the vertical collimation
level should be adjusted.
Adjustment. To adjust the vertical level, com-
pute the correct vertical circle reading by apply-
ing one-half of the index error of the vertical
circle to the direct heading. If the sum of the
two readings is greater than 6,400 mils, subtract
one-half the index error from the direct reading;
if the sum is less than 6,400 mils, add one-half
the index error to the direct reading. Place the
instrument in the direct position and accurately
sight on the point. Using the coincidence knob,
set the fractional part of the correct vertical
circle reading on the micrometer scale, and then
obtain coincidence on the main scale at the
correct vertical circle reading by using the colli-
mation level tangent screw. With the telescope
sighted on the point and the correct reading on
the vertical circle, the ends of the collimation
ARMY TM 5-6675-308-34
MARINE CORPS TM 08837A-34/2
level bubble will not be aligned. Align the im-
ages of the ends of the collimation level bubble
by using the two capstan adjusting screws lo-
cated immediately below the collimation level.
When adjusting the bubble, rotate both screws
the same amount in opposite directions. After
making the adjustment, tighten the screws by
rotating the screws slightly in opposite direc-
tions, being careful not to change the alignment
of the ends of the bubble. Repeat the test and
adjustment procedure until the collimation level
error is less than 0.05 mil (10”).
Example:
Vertical circle reading for
direct pointing
1,544.400
Vertical circle reading for
reverse pointing 4,856.098
Sum 6,400.498
Apparent index error = 6,500,498 – 6,400 =
100.498 mil
Collimation error
= 100.498 – 2 –0.249 mil
Correct vertical circle reading (direct) = 1,544.400
– 0.249 = 1.544.151
With the telescope in the direct position, accurately
sight on the point. Set the fractional portion of the
correct scale reading on the micrometer scale by using
the coincidence knob, and then obtain coincidence on
the main scale at the correct vertical circle reading
(1,544.151) by using the collimation level tangent
screw. Bring the split bubble into coincidence by turn-
ing its adjusting screws.
5-20.
NOTE
This adjustment can also be made with
the telescope in the reverse position, us-
ing the mean value for the reverse point-
ing, i.e., 4,856.098 – 0.249 = 4,855.849
roils.
Other Adjustments. Other adjustments to the
theodolite that ‘may be required periodically are as
follows:
a. Leveling Screws. The three leveling screws must
turn smoothly and with moderate ease and with-
,
out any shake or backlash. To tighten or loosen
the movement of the leveling screw, use the
capstan adjusting screw located immediately
above each leveling screw.
b. Tangent Screws. The tangent screws must turn
easily and smoothly, without backlash, through-
out their travel. A capstan adjusting ring is
located immediately behind each tangent screw,
To adjust the tangent screws, rotate the adjusting
ring with an adjusting pin.
5-13