B4- 30 RELEASE AND RECORDER RECORD 
be required because of missing relative humidity on the first release, 
the first release will be evaluated and the reason for not making a second 
release will be entered in the remarks portion of WBAN-31A. 
9. Drift_and Shift Corrections. The following paragraphs explain the 
method of applying drift and shift corrections to the temperature, humid- 
ity, and hypsometer traces of the recorder record. 
9.1 Contact Numbers and Drift Line. At each high and low-reference 
contact, write the contact number (5, 10, 15, 20, etc.) to the right of the 
reference trace, provided that the contact number is a multiple of 5. 
Connect each successive recorded low-reference contact witha straight 
line, termed the ''drift line'', drawn from the upper left edge of the lower 
low-reference contact to the lower left edge of the succeeding one, re- 
gardless of whether intervening low-reference contacts are missing. 
This procedure will be altered as explained in the following paragraphs 
if a shift has occurred between successive low-reference contacts (see 
JB4-9.4 and 9.5). 
9.2 Entry of Low Reference Drift. At the bottom and top of each low- 
reference contact, and immediately to the left of it, enter to tenths of 
ordinates, with proper sign prefixed, the difference between the low- 
reference trace and the ninety-fifth ordinate. If the difference is zero 
enter 0. This difference is termed 'low-reference drift correction." 
Entry of the low-reference drift correction at low-reference contacts 
may be omitted beginning with the point on the record where low refer- 
ence replaces the humidity contacts. The low-reference drift correction 
will, however, continue to be entered at each significant level. 
9.3 Low Reference Drift for Surface Level. Draw the drift line verti- 
cally, that is, parallel to the printed ordinate lines from the lower left 
edge of the first low reference after release to the surface level, unless 
there is evidence to indicate that there has been a shift between release 
and first low reference. This may be indicated by an abrupt shift in the 
temperature trace. 
9.4 Shift of all Elements. If the record indicates that there has been 
an abrupt shift (proportional), draw the drift line accordingly. Inspect 
the record to determine that there has been a shift of all elements and 
that the shifts are proportional to their ordinate values. Determine care- 
fully that there has not been an independent shift of the temperature 
trace. Note: A proportional shift in each direction may occur between 
successive low-reference traces such that the shift does not show up in 
examining the reference traces. 
Lo -@Y) FMH#3 
