Figure 9-5.The Schrader gauge.
to all hands. We plan or cancel operations on the
basis of weather predictions. Accurate weather
forecasts are made only after a great deal of
information has been collected by many observers
located over a wide area.
One of the instruments used in gathering
weather data is the barometer, which measures
air pressure. Remember, the air is pressing on you
all the time. Normal atmospheric pressure is 14.7
psi. As the weather changes, the air pressure may
be greater or less than normal. Air from high-
pressure areas always moves toward low-pressure
areas, and moving airor wind-is one of the main
causes of weather changes. In general, as air
moves into a low-pressure area, it causes wind,
rain, and storms. A high-pressure area usually
enjoys clear weather. Ships use two types of
barometers to measure air pressure: aneroid and
Figure 9-6.Diaphragm pressure gauge.