B2-20 
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PREPARATIONS FOR SOUNDING 
Determine from the calibration chart the pressure corres- 
ponding to the ''make,"' or beginning, of the nearest contact in 
the direction of higher pressure than pressure (1). Read this 
value from the calibration chart as pressure (2). 
Subtract pressure (1) from pressure (2) to obtain the difference 
in millibars between the beginning of the contact and the baro- 
switch setting pressure. 
Determine from the calibration chart the pressure corres- 
ponding to the 'make,"' or beginning, of the next contact to- 
wards lower pressure. Record this value on the calibration 
chart as pressure (3). 
Subtract pressure (3) from pressure (2) to obtain the number 
of millibars per contact. 
Turn the commutator adjustment screw (detent screw) until 
the contact point rests at least two contacts to the left (high 
pressure side) of pressure (2). Turnthe screw gently counter- 
clockwise and exert no force on the commutator frame. 
Turn the detent screw slowly clockwise to the ''make,"' or be- 
ginning, of the contact corresponding to pressure (2). This is 
the point at which the audio signal switches from temperature 
to humidity o- reference. 
As soon as the signal changes to indicate the ''make,"' or be- 
ginning, of the contact, begin to count the clicks and continue 
to turn the detent screw until the ''make,'' or beginning, of the 
succeeding contact is reached. The complete contact will en- 
compass a humidity (or reference) signal and a temperature 
signal. Record the number of clicks per contact on the cali- 
bration chart. 
Repeat steps (f), (g), and (h) above and take the average of the 
number of clicks per contact. 
Multiply the average number of clicks per contact by the dif- 
ference in millibars (pressure (2), minus pressure (1)) and 
divide by the number of millibars per contact (pressure (2) 
minus pressure (3)). This gives the number of clicks between 
the beginning of the contact (pressure (2)) and the baroswitch 
setting pressure (1). 
F MH#3 
