Table 3-1. Constants Used in Construction and Calibration of Mercurial Barometers

TM 9-6685-202-14

Table 3-1. Constants Used in Construction

and Calibration of Mercurial

Barometers - Continued.

DATA

VALUE

1 mb

0.75006 mm of mercury at

0 and standard gravity.

1 mm of mercury at 0 and

1.3332 mb

standard gravity.

1 mb

0.029530 in. of mercury at

0 and standard gravity.

1 in. of mercury at 0 and

standard gravity.

33.864 mb

Density of clean mercury at 0

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

3-10. 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 A-1

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 temperature-gravity scale

which is aligned with a main scale line. Thus, in figure

is calibrated in degrees centigrade and cm/sec2. The

3-5 the 4 line of the vernier scale is aligned with a line

altitude scale is used in calibrating altimeters and is

on the main scale. The entire reading is, therefore,

described in paragraph 3-13. On the millimeter scale,

632.4 mm.

figure 3-5, only every tenth line is numbered and the

final zero is omitted. Thus the 630 mm line is numbered

(3) From inspection of figure 3-5, 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

5-vernier 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 4-vernier scale line would

to top. Thus in figure 3-5, 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

nor

the

3-10