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A–11
Magnetic bearing
Bearing relative to magnetic north, with the
compass bearing corrected for deviation.
Magnetic variation offset
The location of the magnetic north pole is
different from the geographical north pole.
This causes a difference between the true and
magnetic north direction. This difference is
called magnetic variation, and varies with
respect to the observation point on the earth.
This variation may be entered automatically
or manually.
Navigation calculation
The GPS receiver calculates the range, bearing
and cross track error to next waypoint when
you select a destination. The calculation of
that data is called navigation calculation. The
calculation itself is done using one of two
methods (selectable): Great circle (straight
line between two points) or Rhumb line
(straight line between two points on nautical
chart).
NMEA 0183
The National Marine Electronics
Association's signal format which enables
connection of electronic equipment of
different marine electronics manufacturers.
Plotting interval
The plotting interval determines both how the
track will be reconstructed on the display and
track storage time. The shorter the interval the
more accurate the reconstruction of track line,
however total storage time is reduced. The
plotting interval can be selected to time or
distance. Plotting by distance offers the
advantage that the track is not stored when
the vessel is anchored.
Route
A series of waypoints leading to the ultimate
destination.
Route navigation
Following a stored route.
S/A
GPS was developed by the US Department
of Defense mainly for use by its marine
vessels and aircraft. For civil users the
accuracy of the system is purposely
downgraded for national security reasons.
This intentional accuracy reduction is called
S/A. Because GPS position error may be
greater than 100 meters any GPS position
should be double checked against other
sources to confirm position.
Skip
This means to bypass a waypoint in a route.
Storage capacity
Storage capacity defines how many points of
track and marks a memory can hold. The GP-
80's storage capacity is 2,000 points.
Time-to-go (TTG)
The amount of time necessary to get to a
destination, maintaining current speed and
course.
Time differences
Time differences (or TDs) are the position
information generated by the Loran C and
Decca position-fixing systems. TDs are the
time in microseconds between the
transmission of pulsed signals in the Loran C
and Decca systems.
Total distance
Total distance is the number of miles from
starting point to end point in a route.