

TM 9668520214
C1
Table 31. Constants Used in Construction
and Calibration of Mercurial
Barometers  Continued.
DATA
VALUE
1 mb
0.75006 mm of mercury at
0 and standard gravity.
C
1 mm of mercury at 0 and
C
1.3332 mb
standard gravity.
1 mb
0.029530 in. of mercury at
0 and standard gravity.
C
1 in. of mercury at 0 and
C
standard gravity.
33.864 mb
Density of clean mercury at 0
C
Assumed to be 13.5951 grams
per cubic centimeter at
pressure of one atmosphere.
Standard gravity
980.665 cm per second per
second.
1 Standard atmosphere
1013.250 mb,
760 mm Hg (standard),
29.9213 in. Hg (standard),
14.6960 psi.
mm = millimeter(s)
cm = centimeter(s)
in. = inch(es)
mb = millibar(s)
psi = pounds per
m = meter(s)
square inch.
C = Celsius
(Centigrade).
(2) The number of tenths of a millimeter, in
310. Reading the Barometer Scale
addition to the number of whole millimeters, is found by
looking along the vernier scale and noting which line of
a. Type A1
the vernier scale is aligned with a line on the main scale.
(1) The left side of the scale is calibrated in
Except for 0 and 10, there can be only one vernier scale
millimeters of mercury from 0 to 790. The right side of
line aligned with a main scale line at any given position
the scale is calibrated in thousands of feet altitude from
of the vernier slide. The number of tenths of a
1,000 to +80,000 feet. The applied correction scale is
millimeter is the number of the line on the vernier scale
calibrated in millimeters. The temperaturegravity scale
which is aligned with a main scale line. Thus, in figure
is calibrated in degrees centigrade and cm/sec2. The
altitude scale is used in calibrating altimeters and is
on the main scale. The entire reading is, therefore,
described in paragraph 313. On the millimeter scale,
632.4 mm.
final zero is omitted. Thus the 630 mm line is numbered
(3) From inspection of figure 35, it will be
63. The number of whole millimeters is read at the last
apparent that if the vernier slide was raised 0.1 mm, the
line on the main scale which the 0 line on the vernier
5vernier scale line would coincide with the scale line it
scale has passed. The main scale is read from bottom
is now slightly below, and the 4vernier scale line would
to top. Thus in figure 35, the 0 line is slightly above
be slightly above the scale line with which it now
632 on the main scale.
coincides. However, if the slide were raised less than
0.1
mm,
neither
the
4
nor
the
5
310

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