PREPARATIONS FOR SOUNDING B2-95 
should be notified. During the zero and sensitivity check recordings, the 
recorder record must feed out normally and must not be fed out manu- 
ally. 
3.1 Zero Recordings. One-half inch zero recordings will be made be- 
fore and after the sensitivity check. Zero recording of at least one- 
eighth of an inch in length will follow the low reference and baseline- 
checks. If a hypsometer radiosonde is used, the hypsometer check will 
be followed by a zero recording of at least one-eighth of an inch. These 
zero recordings will be made with the recorder record feeding out norm- 
ally. If more paper is needed, it may be fed out manually. 
3.2 Sensitivity Check. The recorder sensitivity check will be taken 
before the baseline-check and will be submitted as part of the recorder 
record pertaining to each radiosonde observation. Instruction for taking 
a satisfactory sensitivity check will be found in the ground equipment 
section of the instructions issued by the separate services. 
3.3 Low Reference Check. After the sensitivity check has been com- 
pleted, the recorder will have been adjusted tothe correct 60 or 120 Hz 
value, After the appropriate amount of zero recording, connect the blue 
and black test leads. Turn the INPUT or SIGNAL SELECTOR recorder 
switch to the X or SIGNAL position. Record about 10 seconds of the un- 
adjusted low reference signal. Ifthe low reference signal, after recorder 
corrections have been applied, is received at or above 89.0 ordinates 
but below 100.0 ordinates, the radiosonde is acceptable. In this case 
adjust the low reference to recordat 95.0 ordinates after the 10 seconds 
of the unadjusted trace have been obtained. Ifthe signal is received out- 
side these limits, recheck the battery voltage; if the battery voltage is 
within limits (see Table B2-1), reject the radiosonde. The low reference 
check will be submitted as part of the recorder record pertaining to each 
radiosonde observation. 
3.4 Hypsometer Check. If a hypsometer radiosonde is used, a hyp- 
someter check (see §B1-2.9) will be taken prior to the baseline-check 
(after the low reference check) and submitted as part of the recorder 
record pertaining to each radiosonde observation. If the radiosonde is 
equipped with a hypsometer (green) test lead, the bare portion will be 
cut off before the baseline- check (see JB2-14.1). Aninvalid baseline will 
result if this lead should accidentally be used instead of the low reference 
lead. 
4, Radiosonde _Baseline-Check Boxes. The baseline- check box pro- 
vides a method of securing stable temperature and relative humidity 
conditions during the baseline-check. The box contains a radiosonde test 
switch, ventilation fan, psychrometer, humidity control tray andin some 
models an internal radiosonde instrument power supply. 
1-1-69 FMH#3 
