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Page 72 491 Echo Sounder Operations Manual
longitude Imaginary lines on the Earth's surface running North/South
and expressed in degrees (0-180) east or west of the Prime
Meridian (a line running from the North to South Pole, passing
through Greenwich, England).
meter A unit of measurement (length) equal to 39.37 inches, slightly
more than a standard yard.
nautical mile (nm) An international unit equal to 6,076.115 feet (1,852 meters)
used officially in the U.S. since 1959. A nautical mile is about
800 feet more than a statute mile. One nm is equal to 1
minute of latitude.
ping A pulse transmitted from the 491 echo sounder. Also, the act
of transmitting a pulse from the echo sounder ("pinging").
SOG Speed Over Ground. The actual speed of your vessel relative to
the earth, not the water.
tide The vertical rise and fall of water caused by the gravitational
pull of the moon and sun.
transducer The device mounted through the hull to send and receive
ultrasonic beams that determine seabed conditions and locate
fish.
waypoint A particular location, saved by marking fish on the echo
sounder’s LIVE-DATA screen, which is used as an intermediate
or final destination.