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961 Operations and Reference Manual Rev. D
The GPS SATELLITE STATUS screen shows the received Sig-
nal-to-Noise Ratio (SNR) for each satellite (up to 12), and a map
indicating where the satellites are now located in the sky. Sat-
ellites are identified by their pseudorandom number (PRN), a
two-digit number assigned by the U.S. government. The center
of the satellite map represents the center of the sky, and the
outer ring is the horizon. The view is looking down from
above, with East to your right and West to your left.
Also displayed on the screen is the following GPS data:
•
ACCURACY
•
HDOP (horizontal dilution of precision)
Accuracy is the estimated accuracy of the GPS system to be
expected at the current time. Your position readings should be
more accurate than this estimate 95 percent of the time.
HDOP is a technical measure of how good the satellite pattern
is in the sky for fix-taking purposes. HDOP depends on how
many operational satellites are in view and where they're cur-
rently located. HDOP is calculated from the satellites' current
positions, not on actual received signals, and doesn't consider
atmospheric conditions, Selective Availability, and signal inter-
Chapter 5 - Understanding Position Coordinates
GPS satellite status screen
Page 5-3
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