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North, Magnetic:
North is the principle reference point of the compass (i.e. North is
000°). Magnetic North relies on the earth’s magnetic field to align a metal pointer
generally towards True North. However, due to local variations in the earth’s
magnetic field around the globe, the difference between True North and Magnetic
North can be greater than 10°. See
True North
.
North, True:
North is the principle reference point of the compass (i.e. North is
000°). True North uses the axis of the rotation of the earth as the reference for
North and is constant for all points on the earth. Most GPS units default to True
North as the setting. The GPS heading may vary from the boat compass heading
because the compass uses Magnetic North. Humminbird® GPS units provide the
option of selecting True or Magnetic readouts by using the North Reference menu.
See
Magnetic North
.
Present Position:
Present Position is the current location (latitude, longitude)
determined by GPS. The Present Position is indicated on-screen by a directional boat
icon if the boat is moving, or a round symbol if the boat is stationary.
Route:
A Route is series of waypoints linked together in a specific sequence to define a
navigation path between two points, and saved in the fishfinder’s memory. Routes are
often used when frequently traveling between two or more locations because it is a faster
and more accurate method than repeatedly selecting individual waypoints each time one
travels through the same area. Routes consist of a Start Waypoint, an End Waypoint, and
a series of waypoints in between. Users can begin navigation at the beginning, the end (to
run the route in reverse) or at any waypoint in between. See
Waypoint
.
SD:
SD is an acronym for Secure Digital. An SD card is virtually identical in function
to an MMC; however, the speed at which information can be accessed is generally
faster, the storage capacity is generally larger, and the card has security features
which can be used to prevent extracting the data from the card. SD is the same
format that many digital cameras use. See
MMC.
Selective Availability:
Selective Availability (SA) is a GPS system “feature” that can be
implemented by the U.S. Department of Defense (DoD) to degrade the accuracy of
GPS positioning information. With SA active, the GPS is accurate to within 100 meters
95% of the time. With SA inactive, the GPS is accurate to within 45 meters 95% of the
time. Currently, SA is inactive and the consumer can enjoy the greater precision GPS
provides; however, the DoD reserves the right to activate SA at any time.
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Speed Over Ground (SOG):
Speed Over Ground is the measurement of the boat’s
progress across a given distance, and is the speed measurement provided by GPS.
An alternate, Speed Through Water, is provided by a speed paddlewheel, and is the
measurement of the flow past the boat, which may vary depending on current
speed and direction. Speed Over Ground is optimal for navigation because accurate
destination times can be derived from this measurement. Humminbird® products
allow for input and display of both speed measurements.
Time To Go (TTG):
Time To Go is the estimated time required to reach the
destination waypoint. TTG is calculated using the SOG and DTG. See
SOG
and
DTG
.
Track:
A Track is a series of saved points that define the past path of the boat. These Track
Points are saved at regular time intervals. Tracks are a useful and quick method to see
where you’ve been, and an easy guide to follow to get you back to the starting point.
Generally, all GPS units have a limited number of Track Points that can be saved before
the unit runs out of memory and begins erasing the first track points saved. Because of
this, the user can adjust the Track Point Interval menu to increase the amount of time
between when points are saved, and thus extend the distance covered by a track. Tracks
can also be permanently saved to memory, and re-displayed at the user’s option.
Track Line (TRK):
The Track Line is the desired line of travel between two waypoints,
and represents the most efficient path between the two points because it is a
straight line. The TRK is measured in degrees (i.e. 321°, where 000° is North, 090°
East, 180° is South, 270° is West). See
Cross Track Error
and
Course Over Ground
.
Trackplotter:
Trackplotter describes a navigation device that shows Present Position,
along with Track, Waypoint, and Routes, but NO MAP in the background. See
Chartplotter
.
Trolling Grid:
Trolling Grid is a Humminbird® feature that displays a precise
reference grid around a waypoint. This grid is used as a guide pattern for trolling
around a specific area to assure a more efficient and complete coverage of that area.
Trolling Grid resolution be changed by zooming in or out on the chart. The Trolling
Grid can also be rotated on the display to orient it for optimal boat course for wave
and wind conditions.
UTC:
UTC is an acronym for Universal Time Constant. UTC is the “standard time” used in
navigation, and is the local time in Greenwich England. (UTC is equivalent to Greenwich
Mean Time (GMT)). To display the correct Local Time in a Humminbird® GPS unit, the
user must use the Local Time Zone menu and select the time zone (i.e. EST, CST).
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