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|  MIL-M48557A(AR)
Center the level vial bubble and take a reading from the gunner
quadrant and record the error, if any. Scribe an index line on
the mount casting nearest to the pitch knob. Place an index
pointer on the pitch knob directly opposite the scribed index
line. The index pointer may be held in place mechanically or
by the use or commercial putty. Turn the
pitch knob one-
half turn and return to the position previously established by
the indices and do not overtravel pointer - index coincidence.
Recenter the gunner's quadrant. The difference (mils) between
the first reading and the second reading is backlash. Backlash
at zero elevation shall not exceed the limit specified in
3.8.5. This test will be repeated in the opposite direction.
4.8.11 Cross level travel. Position the mount as specified
in 3.6 with the Sighting Device 10549200 in the telescope
mounting surface. The pitch and cross level vial bubbles shall
be centered. Position the wall target (see sketch Figure 1)
approximately 40 feet from the objective end of the sight
adapter and turn the cross level knob left until full excursion
has reached the specified travel in 3.8.6. Return to the zero
position. Repeat the above procedure in the opposite
direction. The tolerance lines (excursion limits) on the wall
target (Figure 1) will be used for this test.
4.8.12 Backlash (cross level). With the mount positioned
as specified in 3.6, and install Leveling Adapter,
10558253-11 on the quadrant mounting surface, place a
calibrated Gunner's Quadrant 8658940 on the Leveling Adapter to
measure cant. Center the level vial bubble of the gunner's
quadrant and record the error, if any. Repeat the procedure
for measuring backlash outlined in 4.8.10. Repeat the test for
backlash in the opposite direction and the backlash shall meet
the requirements of 3.8.5.
4.8.13 Mount rigidity. With the mount positioned as
specified in 3.6, sight through the Sighting Device 10549200
and establish a line of sight for zero elevation and zero cant.
A wall target (see sketch Figure 1) shall be placed
approximately 40 feet from the objective end of the sight
adapter with the line of sight superimposed upon the vertical
and horizontal lines of the wall target. Apply the 20 pound
load, as specified in 3.8.8, tangentially to the mount in the
direction of the target. Gradually release the load and record
the movement by observing the displaced vertical line in the
sight device. Re-establish the line of sight to the vertical
and horizontal lines on the wall target as previously performed
at the start of the test. Apply the 20 pound load at the right
side of the telescope support. Gradually release the load and
record the movement by observing the displaced vertical line in
the sight adapter. Mount rigidity shall be as certained by
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