B2-18 PREPARATIONS FOR SOUNDING 
This correction is the ''pressure contact setting'’ correction 
and will not be entered on WBAN-31A. The pressure will not 
be corrected for a difference in altitude of less than 3 meters. 
Elevation and Elevation of the Radiosonde 
Difference in Altitude Correction 
(meters) (millibars) 
(=) 
NEOCDYN RMA 
3 
4 
9) 
6 
7 
8 
9 
0 
— 
= = 
The table is based on the relationship of 1 millibar per 8.5 meters dif- 
ference in elevation. Add the correction to the station pressure when the 
elevation of the radiosonde is lower than the station elevation, and sub- 
tract it when the radiosonde is higher. In some cases, the station ele- 
vation differs from that of the actual altitude of the barometer. Under 
these circumstances, use the altitude upon whichthe pressure reduction 
tables are based to compute the difference referred toJB2-15.1.The 
pressure contact setting as determined in JB2-15.5 is the setting of the 
baroswitch before release and will not appear on WBAN-31A. if the 
elevation of the radiosonde at contact setting and the release elevation 
differ by 3 or more meters (see JB4-4.3). 
15.2. Calibration Chart. A chart indicating the pressure calibration 
values is supplied with each radiosonde (see §B1-1.1). Check all cali- 
bration charts for uniformity; e.g., all contacts and millibar values must 
be reasonable. Reject the radiosonde when the calibration chart appears 
erroneous, 
15.3 Cleaning the Baroswitch. Clean the baroswitch before making the 
contact setting. The printed commutator should not be polished with 
emery cloth or crocus cloth. All dust and foreign particles should be 
removed by brushing the contact surface of the commutator and the con- 
tact point thoroughly with a camel hair brush, after which the entire 
commutator surface should be wiped firmly with lens tissue, and finally 
brushed again to remove any remaining particles. The brush strokes 
should be parallel to the contacts. Care must be taken not to apply force 
1-1-69 FMH#3 
