PREPARATION OF CHARTS Borz2i 
pressure-altitude curve on WBAN-31C could be based on the 
125, 100, and 82 mb points; ifitterminates at 12 mb, the pres- 
sure-altitude curve on WBAN-31C could be based on the 20, 
15 and 12 mb points; if it terminates at 8 mb, the red pres- 
sure-altitude curve on WBAN-31C could be based on the 12.5 
10, and 8 mb points. 
Whenever the pressure altitude of astandard isobaric surface 
or maximum altitude exceeds or falls below the pressure alti- 
tude scale printed ona chart, displace the pressure altitude 
curve to the right or left, as appropriate, and renumber the 
scale accordingly. 
Whenever the pressure altitude curve is based on estimated 
mean virtual temperature, the estimated portion of the curve 
will be drawn as a solid line through missing or doubtful por- 
tions of the record. 
Whenever the station pressure is less than 1000.0 or 850.0 
millibars, the altitude of the corresponding constant- pressure 
surface, as computed on the back of WBAN-31A, will be plot- 
ted, and the pressure altitude curve extended to the 1000 mb 
level. 
10.2 Doubtful Pressure Altitude. Pressure altitude computation will be 
classified as doubtful when the mean virtual temperature is based on a 
doubtful or missing portion of the temperature curve and exceeds the 
following limits: 
MISSING TEMPERATURE 
a. 
be 
Cc. 
d. 
From the surface to 400 mb., 1 km. 
From the surface to 100 mb., 1.5km with (a) satisfied. 
From the surface to termination of flight 2km with (a) and (b) 
satisfied. 
When the tropopause occurs ina missing stratum 1.5 km thick. 
DOUBTFUL TEMPERATURE 
a. 
Do 
Ls hoGy 
From the surface to 400 mb., 2 km. 
From the surface to 100 mb., 3km. with (a) satisfied. 
FMH#3 
