Chapter 2— PRESSURE 



Figure 2-7.— Precision aneroid barometer (ML-448/UM). 



209.93 



mercurial barometer. These differences are 

 logged, and the algebraic mean is computed 

 to determine an acceptable instrument correc- 

 tion. This correction is then posted on or near 

 the instrument and applied to subsequent station 

 pressure readings. Procedures for computing 

 an acceptable precision aneroid barometer cor- 

 rection may be found in the Manual of Barometry 

 or FMH No. 1, chapter A-12. 



Shipboard aneroid barometers should be fre- 

 quently checked for accuracy with a mercurial 

 barometer at a Naval Weather Service 

 unit ashore. Pressure should be reduced to 

 sea level when compared barometers are not at 

 the same elevation (to the nearest foot). In the 

 comparison, care should be taken that the com- 

 parative readings are made simultaneously and 



during a period when the pressure tendency 

 is steady. 



When adjusting the setting of the aneroid 

 barometer, use a small screwdriver and remove 

 one-half of the apparent error on the first 

 adjustment. Tap the case lightly to permit the 

 linkage and index hand to settle to the new 

 setting. Obtain a current station pressure from 

 a corrected reading of the mercurial barometer 

 and note the amount of remaining error in the 

 aneroid. Again adjust to remove one-half of the 

 remaining error, tap the case, and allow the hand 

 and linkage to settle. Do not attempt to adjust 

 for any error less than 0.5 mb. A field main- 

 tenance technician may adjust a precision aneroid 

 to a correction of zero. 



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