PREPARATION OF CHARTS Bpmls 
6. Mean Virtual Temperature. The mean virtual temperature of each 
stratum is found by displacing to the right the dash representing the mean 
temperature of the stratum. Determine the amount ofthis displacement, 
which is based on the mean relative humidity and the mean temperature 
of the stratum, as follows: 
a. Find the distance between the vertical brown tabs bounding the 
extension of the dash denoting the mean temperature. If there 
are no printed vertical brown tabs immediately above or below 
the dash and in the same stratum, or none embracing it, the 
mean virtual temperature will be considered the same as the 
mean temperature. 
b. Estimate the mean percentage of relative humidity for the 
stratum. If the stratum contains missing humidity record, the 
mean will be based on the best possible estimate of the mois- 
ture content of the stratum. 
c. Multiply the distance found in (a) by the mean percentage found 
in (b). 
d. At the distance found in(c), drawadash parallel to, and to the 
right of, the mean temperature dashofthe stratum. The mean 
virtual temperature of the stratum will be read at the dis- 
placed dash. 
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Figure B5 - 5. Mean Virtual Temperature Computation 
1-1-69 FMH#3 
