plastic parts will warp, melt, or shrink. Aboard ship,
stow plastic calculators in an accessible but secure
place. The shock of falling off a plotting table or
desktop in high seas may crack the plastic disks.
CP-402/UM PRESSURE REDUCTION
COMPUTER
The CP-402/UM pressure reduction computer (fig.
2-46) is a two-sided calculator used to compute sea-
level pressure, altimeter setting, and pressure altitude
from station pressure. Detailed instructions for each
process are printed on the calculator.
CP-165/UM PSYCHROMETRIC COMPUTER
The CP-165/UM psychrometric computer (fig.
2-47) is a very colorful, two-sided calculator used to
compute dew-point temperature from air temperature,
wet-bulb temperature, and pressure. One side is used
when the air temperature is above freezing (32°F),
while the other side is used for computations when the
temperature is at or below freezing. The psychrometric
computer may also be used to calculate relative
humidity from air and dew-point temperature, and to
convert between the Fahrenheit and Celsius scales.
Detailed instructions for use are printed on the
calculator and are also published in NA 50-30FR-523,
Handbook, Operation and Care of Aerological
Calculators, Computers, and Evaluators.
CP-718/UM DENSITY ALTITUDE COMPUTER
The CP-718/UM density altitude computer is
shown in figure 2-48. It is primarily used to compute
Figure 2-48.—CP-718/UM density altitude computer.
2-37
