Sony PEGA-CC5 Operating Instructions Manual page 6

About GPS
GPS (Global Positioning System) satellites
continuously emit signals for positioning on
the Earth. As a GPS aerial receives these
signals, users can be informed of their
location (latitude, longitude and altitude)
anywhere on the Earth. Information must be
received from three satellites in order to
obtain two-dimensional fixes (altitude and
longitude), and four satellites are required for
three-dimensional positioning (latitude,
longitude and altitude). As GPS satellites are
controlled by the U.S. Department of
Defense, a deliberate margin of error
between a few feet (a few meters) and 30 feet
(10 meters) exists. As a result, the GPS
navigation system may include an error of
between 30 feet (10 meters) and about 700
feet (200 meters), depending on the
circumstances.
As GPS information is obtained using signal
from satellites, it may be impossible or
difficult to obtain the information when using
the system in the following locations:
Tunnel or underground
Under a highway
Between high buildings
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Between tall trees with dense
foliage