TM 9-1290-357-15
knobs. This orients the zero of the azimuth scale
knob (fig. 13 ) until the elevation level vial bub-
on grid (Y) north. When orientation has been
ble is centered. The angle of elevation of an object
is then indicated by its position on the graduations
completed, clamp the magnetic needle by depress-
ing red plunger button.
along the vertical cross line of the telescope's re-
c. Measuring Vertical Angles. Turn elevating
title.
Section IV.
temperature. When the box is at room tempera-
2-10. General
ture, it may be opened and the instrument re-
In addition to the normal preventive maintenance
moved without condensation forming on it. If
services (para 3-6 through 310), special care
anticondensation chambers are not used and in-
must be observed where extremes of temperature,
struments are brought into a heated room, con-
humidity, and atmospheric conditions are present.
densation will occur and the instruments will
Proper cleaning and storage not only insure pro-
have to be wiped thoroughly dry. Use only lens
per operation and functioning, but also guard
tissue paper for drying lenses and windows.
against excessive wear of the working parts and
deterioration of the materiel.
f. Inspect instruments frequently. When possi-
ble, keep instruments in their cases. To provide
maximum protection for the instruments, the fol-
2-11. Operation in Extreme Cold
lowing should be strictly observed:
Weather
(1) Keep instruments thoroughly clean.
a. In temperatures below freezing, it is neces-
(2) Do not let snow and ice collect on the
sary that moving parts be kept absolutely free
instruments.
from moisture.
(3) Leave no metal surfaces exposed with-
b. Excessive oil on the working parts will con-
out a protective film of lubricant.
geal causing sluggish operation and functioning
(4) Never apply heat from strongly concen-
or complete failure. This applies in particular to
trated sources directly to an instrument. Sudden
focusing parts. Special care should be taken to
changes in temperature will cause optics to break.
eliminate all excess oil.
2-12. Operation in Extreme Heat
knobs with bare hands. Use gloves if possible.
a. Avoid exposing instrument to the direct rays
Frozen fingers or loss of skin may result if this
of the sun which may damage the instrument's
precaution is not followed.
optics. Provide as much cover or shade as possible.
d. Never breathe on a lens in cold weather.
b. When not in use, cover instrument and stow
Frost patterns will form obscuring the image,
in the M6A1 carrying case, to protect it from
and in extreme cases, may even break the lens.
extreme heat.
e. Do not bring any materiel indoors unless
it is absolutely necessary. It is best to leave it
Conditions
outdoors, but covered to protect it from the snow.
Snowtight lockers which stay at outdoor temper-
a. To protect instrument from damage by di-
atures are recommended as a place for keeping
rect exposure to the sun, dust, or sand by erecting
aiming circle. If it is necessary to bring instru-
a vertical barrier (or equivalent).
ments from low temperatures to room tempera-
b. Under extremely dusty or sandy conditions
tures, "anticondensation" containers should be
extra care must be exercised when cleaning the
used. These containers can be specially made boxes
instrument to prevent the dust or sand from da-
or any other reasonably airtight container with
maging mechanical components or scratching
heat-conducting walls. Keep them outside so that
glass or optical surfaces.
they will remain at prevailing temperatures until
it is desired to bring an instrument indoors. Then
c. When not in use, cover and stow instrument
put the instrument into the container, close the
in the M6A1 carrying case making certain that
top, bring it indoors and let it come to room
case is free from any foreign matter.
2-4
