Note. Failure or unsatisfactory performance of equipment will be reported on WD,
AGO Form 468. If this form is not available, see TM 38-250.
a. General. (1) Protect the aneroid against
violent and sudden jolts.
(2) Use care in handling and transporting.
(3) DO not move the instrument unnecessarily.
b. Plastic window. (1) Clean the plastic window that protects the
dial by wiping with a damp cloth and polishing with a soft clean cloth.
Do not use soiled or gritty cloths. An occasional thin coat of wax well
rubbed with a soft clean cloth will help remove any existing scratches
and at the same time provide a protective film to prevent further
(2) If the plastic window becomes wavy when exposed to a com-
bination of high temperature and high humidity, requisition a new one.
20. FIELD INSPECTION AND MAINTENANCE.
Barometers ML-102-(*) are precision instruments whose readings are
generally dependable to 0.7 millibar (0.02 inch of pressure) or better.
Barometer ML-316T/M is usually dependable to one millibar (0.03
inch of pressure) or better. The readings made with these instruments
ordinarily will be considerably more accurate than these tolerances,
provided the barometers are compared periodically with a mercury
barometer (see b below), checked for free, unimpeded action of the
linkage system (see c below), and reset to agree with a mercury baro-
b. Comparison with mercury barometer. (1) To check the accuracy
of the aneroid, compare it with a mercury barometer of known accu-
racy at least once every three months, or at any time the instrument is
dropped, mishandled, or subjected to severe vibrations in transporta-
tion. The indications of the aneroid will be more reliable if this check
is made at or near the average pressure of the station where the aneroid
(2) Hang or set the aneroid barometer at the same level as the
cistern of the mercury barometer.
(a) Barometer M-102-B, ML-102-E, or ML-102-F, must be hung
alongside the mercurial barometer with the dial in a vertical position.
(b) Barometer ML-102-D or ML-316/TM should always be placed
with the dial in a horizontal position.
(3) Read the mercury barometer and apply temperature, gravity,
and instrumental corrections to determine the true station pressure.
Note. In comparing an aneroid Instrument supplied with a millibar scale only
against a standard mercury barometer which is graduated in inches only, convert the
readings of the aneroid into inches of mercury rather than convert the readings of
the mercury barometer into millibars. (One millibar equals 0.02954 inches.)
(4) The difference between the true station pressure and the indi-
cation of the aneroid is the error of the aneroid barometer. If this error
exceeds 3 millibars, it is probable that the mechanism has sustained