Leica MX400 Operating Instructions Manual page 222

Glossary
event will happen 68% of the time. In terms of position update
accuracy, 68 position updates out of 100 will be accurate to
within specified system accuracy.
ROUTE
A route is a sequential list of waypoints describing a planned
voyage. The active route is the route used for the actual
navigation of the vessel.
S/A
See SELECTIVE AVAILABILITY
SATELLITE HEALTH
Go or no-go message for each satellite included in the almanac
data. The message states whether or not the measurements from
those particular satellites can be relied upon for accurate results.
SATELLITE SIGNAL
Transmitted electromagnetic energy from a GPS satellite whose
time of arrival is measured by the navigator to calculate the
position of the navigator antenna.
SELECTIVE AVAILABILITY (S/A)
A system whereby the accuracy of GPS is reduced. S/A is
controlled by the U.S. Department of Defense.
SEMIMINOR AXIS
The distance from the center of the earth's ellipse to the ellipse
surface as measured along the polar axis. It is identified
symbolically with the letter B, and it varies according to the
reference datum used for position coordinates.
SENSOR
A device that detects a change in a physical stimulus and turns it
into a signal which can be measured.
SET AND DRIFT
The direction and the speed of the water over ground (current).
SIGNAL-TO-NOISE RATIO (S/N)
Quantitative relationship between the useful and non-useful part
of the received satellite signal. A high S/N indicates a good
Version 3.3
Operator's Manual
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