Table 4-2. Applied Correction Vernier Readings (mm)

TM 9-6685-202-14

scale on the vernier slide, indicates the direction and

table 4-2. The applied correction in each case should

magnitude of the correction being applied. The applied

agree with the computed values within 0.10 mm of

correction indicated is the combined total of the gravity

mercury.

and temperature correction. This correction can be

d. Removing an Air Bubble from the Tube (Type A-

checked against predetermined values as follows:

1 only). After a period of time, an air bubble will

(1) Adjust the gravity index to standard

accumulate above the mercury in the tube. The bubbles

gravity (980.665), using the two screws holding the

can be forced out through the valve subassembly in the

temperature-gravity scale, figure 1-3.

top of the tube by the application of an external pump

pressure. During the first several weeks of operation,

(2) Set the temperature index to 10C.

this air bubble should be removed at the beginning of

(3) Position the vernier slide assembly at

each day the barometer is in use. Later, once a week

each of the settings given in table 4-2 and note the

will be sufficient. Since the bubble removal procedure is

correction indicated at each setting.

simple and requires little time, its use at more frequent

(4) Repeat (3) above for temperature settings

intervals than that specified above, is desirable. When

given in table 4-2.

removing an air bubble use the following procedure:

(5) Compare the values of the indicated

applied correction with the computed values given in

Table 4-2. Applied Correction Vernier Readings (mm)

MODEL 10-00-00-F

SCALE

TEMPERATURE SETTING (G RAVITY MUST BE

READING

SET AT 980.665).

MM.

10C

20C

25C

30C

40C

770

+1.95

+.65

-.65

-1.95

670

+1.71

+.57

-.57

-1.71

570

+1.46

+.49

-.49

-1.46

470

+1.22

+.41

-.41

-1.22

370

+.98

+.33

-.33

-.98

270

+.73

+.24

-.24

-.73

170

+.49

+.16

-.16

-.49

+.24

+.08

-.08

-.24

+.07

+.02

-.02

-.07

thereby making it unnecessary to readjust the amount of

(1) Connect the vacuum pump to the tube

mercury above the valve.

However, if additional

evacuation nipple.

mercury is forced up, readjust the mercury to the orange

(2) After the pump has run for approximately

calibration line in accordance with paragraph 3-5 (2).

1 minute, apply enough pressure to the cistern by

CAUTION

means of the hand blower (furnished in the barometer

When removing air bubble, extreme

drawer) to force the mercury up to the top of the tube.

caution should be exercised to avoid

As the mercury nears the top, if there is air in the tube, it

forcing mercury into the vacuum

will be seen escaping through the mercury above the

sealing ball. It is not necessary to open the tube seal

system.

valve. Considerable pressure may be applied to the

cistern without forcing additional mercury past the valve,

4-7