RELEASE AND RECORDER RECORD B4-7 
should be entered on Form WBAN-31A in the surface observa- 
tion block, in terms of whole °F, and the equivalent °C will be 
entered to the nearest tenth of degree. Relative humidity and 
dewpoint temperature should be computed using the Fahrenheit 
readings. 
b. The hygrothermometer yields values of temperature and dew- 
point. The temperature should be entered on Form WBAN-31A 
in the surface observation block, in terms ofwhole °F, and the 
equivalent °C will be entered to the nearest tenth of degree. 
The relative humidity should be computed using the tempera- 
ture and dewpoint readings (°F). Entry ofavalue for wet-bulb 
temperature may be omitted. 
4.4.1 Ventilated or Sling Psychrometer. Ifatelepsychrometer or hygro- 
thermometer is not available or is inoperative, the ventilated or sling 
psychrometer will be used to obtain the temperature at release. Enter 
the dry and wet bulb readings in degrees and tenths as indicated in the 
following paragraphs. 
a. If the thermometers are calibrated in degrees Celsius and a 
psychrometric calculator is available to compute relative hu- 
midity using Celsius temperature, then the temperatures will 
be entered directly on WBAN-31A without conversions. Ifa 
psychrometric calculator isnot available, table 4inthe Radio- 
sonde Observation Computation Tables (WBAN) may be used 
to compute relative humidity. 
b. If the thermometers are calibrated indegrees Fahrenheit, the 
relative humidity will be computed using those temperatures 
directly by means of apsychrometric calculator. The dry bulb 
temperature willbe convertedto°C. Entries onWBAN-31A will 
include both °C and °F for the dry bulb and °F for the wet bulb. 
4.5 Relative Humidity. Compute the relative humidity in accordance 
with §B2-7.1. When the wet-bulb is covered with water and a depression 
cannot be obtained, the relative humidity will be regarded as 100 percent 
and the dewpoint the same as the wet-bulb. If the wet-bulb is covered 
with ice and a depression cannot be obtained, the relative humidity will 
be regarded as 100 percent with respect to ice and its water equivalent 
determined, as indicated on the psychrometric calculator, when the dry- 
bulb is less than 0°C, except that whenever liquid fog is present at the 
station and no depression is obtainable, it will also be regarded as 100 
percent with respect to water. The surface relative humidity will not be 
calculated when the surface temperature is colder than -35°F or -37.2°C. 
Enter the relative humidity to the nearest whole percent, on WBAN-31A. 
TEES (6X) F MH#3 
