b. For reading at night, illuminate the dial using the switch on the side of the case. The intensity of light may be
regulated with the rheostat. Remove the batteries when altimeter is not in use.
Caution: Be sure to cushion the altimeter against road shock and avoid sudden jarring at all times.
Operating Sling Psychrometer
The sling psychrometer is the accessory which provides the wet and dry bulb thermometer readings for the air
temperature and relative humidity correction factors. Remove the instrument from the cover of the altimeter and proceed
a. Slide the handle off the thermometer as far as possible.
b. Rotate the thermometer head 1800 and the handle 90° on its end of the link.
c. Saturate the wick on the wet bulb thermometer with water.
d. Hold the handle of the psychrometer in one hand with the link and thermometer assembly at right angles.
Rotate the thermometers two or more revolutions per second for at least one minute.
e. Read and record the temperature of both thermometers. Repeat until two successive readings agree.
Refer to section VIII for the use of these readings in obtaining the air temperature and relative humidity
correction factor. Section VIII explains the use of the various charts and tables.