TM 5-6675-250-10
2-7. OPERATING PROCEDURE - Continued
OPERATION
Place the MODE SELECT switch (1) to BIAS (2) (audible click).
a.
When operating in the dark, light from the cage-uncage indicator is visible
at 45 meters. The indicator should be shielded to avoid detection when
security is required.
Rotate the CAGE-UNCAGE knob (8) on the reference unit (9) clockwise until the UNCAGE indica-
b.
tor (10) lights.
Observe TEST METER pointer (3) swing left and right from zero, at a rate of about one reversal
c.
every five seconds. When the pointer comes to a stop, verify that it is positioned at zero; if neces-
sary use the BIAS control (4) to obtain the required position. This is done by rotating the outer
ring counterclockwise to unlock the inner knob, rotating the inner knob to the pointer, and rotat-
ing the outer ring clockwise to relock the inner knob.
Rotate the CAGE-UNCAGE knob (8) on the GRU (9) counterclockwise until the UNCAGE indicator
d.
(3) is out (audible click).
Place the MODE SELECT switch (1) to GC (gyro compass) (5); verify that the GYRO SYNC indica-
e.
tor (6) illuminates within two minutes at normal ambient temperature (above + 15F (+9.4C)).
During the first azimuth determination on a new site, the operator should
ensure the follow-up index mark does not remain at either end of the servo
operation range. Continuous operation of the instrument in this condition
could cause excessive magnetic anomalies, which cause the GRU to be
preoriented in excess of 40 degrees of true north.
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