Install guide

ARMY TM 5-6675-308-34
MARINE CORPS TM 08837A-34/2
eliminated, the crossline will remain fixed on the object
as the eye is moved. If all parallax has not been elimi-
nated, the crossline will appear to move back and forth
across the object. To eliminate any remaining parallax,
change the focus of the eyepiece slightly to bring the
crosslines into sharper focus, and refocus the telescope
accordingly until there is no apparent motion, Each
time an angle is to be measured, the telescope should
be focused to eliminate parallax, since accurate point-
ings with the instrument are not possible if parallax
exists.
e. Setting Up the Target Set. The procedure for
setting up the target set is as follows:
(1) Remove the tribrach and target from the case.
(2) Secure the target to the tribrach.
(3) Attach the target to the tripod by screwing the
fixing screw snugly into the base of the tri-
brach.
(4) Plumb and level the target in a manner similar
to paragraph 5-4c.
(5) Rotate the target so it faces the theodolite.
5-5. Horizontal Circle Readings. (See figure 5-3.) On
the roil-graduated theodolite, the main scale (upper
window) is graduated in 2-mil increments. Each fifth
graduation is numbered, omitting the unit digits; e.g.,
10 roils appear as 1; 250 roils as 25; and 3,510 roils as
351. The micrometer scale (lower window) is graduated
from 0.000 mil to 1.000 roil. Each 0.002 mil is marked
with a graduation, and each fifth graduation is num-
bered (hundredth of a roil). The scale may be read to
0.001 mil by interpolation. To determine a reading on
the horizontal circle:
a.
b.
c.
d.
Rotate the circle selector knob until the black
line on the face of the knob is horizontal.
Adjust the horizontal circle illuminating mirror
so that both windows in the circle reading mi-
croscope are uniformly lighted. If there is insuf-
ficient light, replace the mirror with a lamp
assembly.
Focus the microscope eyepiece so that the grad-
uations of the circle and micrometer scale are
sharply defined.
Observe the images in the microscope. Bring the
circle graduations into coincidence at the center
of the upper window by turning the coincidence
knob, When the knob is turned, the images of
the opposite sides of the circle appear to move
in opposite directions across the upper window
in the circle-reading microscope. The image of
the micrometer scale in the lower window also
moves. The graduations of the circle (upper
window) are brought into coincidence so that
they appear to form continuous lines across the
e.
f.
g.
h.
i.
dividing line. The center of the field of view in
the upper window is marked by a fixed vertical
index line. The final coincidence adjustment
should be made between circle graduations in
the vicinity of this index line, The line is not
used in reading the circle, The final motion of
the coincidence knob must be clockwise.
Determine the first erect numbered graduation
to the left of the index line that marks the center
of the upper window. This numbered graduation
indicates the value of the circle reading in tens
of roils. In figure 5-3, this value is 121.
Locate on the inverted scale the graduation for
the number diametrically opposite 121 (the num-
ber +320). This number is 441 (viewed
The inverted number is always to the right of the
index line which marks the center of the field of
view. When the unit roils of the circle reading is
zero, coincidence is obtained with the circle
reading and its diametrically opposite number in
coincidence with each other in the immediate
vicinity of the index line, Both values always end
in the same number — in this case, the number
1.
Count the number of spaces between gradua-
tions from 121 to the inverted 441. There is one
space, representing 1 roil. Each of these spaces
represents 1 roil.
Convert 121, which is tens of roils, to 1,1210
roils, and to this value, add the unit roils deter-
mined in c above (1,210 + 1 = 1,211 roils, the
angular value obtained from the main scale).
On the micrometer scale (lower window), the
index line that marks the center of the field also
indicates the value to be read from the microme-
ter scale. This value is 0.403 roil.
Add the values determined in h and i above
(1,211 + 0.403)
=
1,211.403 roils, the angular
value displayed in figure 5-3.
5-6. Setting the Horizontal Circle. The horizontal
circle can be set to read a given value with the tele-
scope ointed at a target. The initial circle setting of
0.150 ±0. 100 mil) is used as an example.
a. Point the instrument at the target.
b. Using the coincidence knob, place a reading of
0.150 on the micrometer scale.
c. Using the scale-setting knob, zero the main scale
as accurately as possible, insuring that the num-
bered lines, which are 3,200 roils apart (the erect
0 graduation and the inverted 320 graduation),
are touching each other.
d. With the coincidence knob, bring the main scale
graduations into a more precise coincidence.
5-7