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