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Fix Type: Fix Type indicates whether the GPS receiver is providing 2D fix or 3D fix. A
2D fix requires only three satellites and provides only latitude and longitude. A 3D fix
requires four or more satellites, and provides latitude, longitude and altitude.
GPS: GPS is an acronym for Global Positioning System. GPS provides accurate
position (latitude, longitude, altitude) information virtually anywhere on the earth
through satellite technology and personal receivers on the ground. A series of
geosynchronous satellites broadcast a unique signal toward the earth once per
second. A GPS receiver, such as that included with many Humminbird® products,
receives the signals from these satellites and is able to determine position based on
very slight differences in the time each signal is received and the receiver’s
knowledge of the location of each of the satellites.
Heading: Heading describes the direction the boat is pointing and is measured in
degrees (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is West). Due to
wind and waves, the boat is often traveling in a slightly different direction than it is
heading, and therefore Heading is often confused with Course Over Ground. See
Course Over Ground.
Map Datum: A Map Datum refers to a particular survey of the earth’s surface that
was referenced when creating a chart (i.e. WGS84). Since the earth is not flat, and
not even consistently round, a mathematical model must be used to translate
coordinates from the sphere of the earth to the flat surface of a chart. This
mathematical model is the Map Datum. Historically, many different Map Datums
have been used around the world to create maps; often a reference to the Map
Datum can be found in the legend of a paper map. It is important to select the
correct Map Datum setting in your fishfinder when comparing GPS position to a
paper chart to avoid slight position inaccuracies. Almost all electronic charts use the
WGS84 Map Datum and therefore, they do not require setting changes.
MMC: MMC is an acronym for Multi Media Card. An MMC is a postage stamp-sized
memory device used to store electronic data such a maps, waypoints, routes and
other information. MMC is a very rugged format suitable for the marine
environment, but it is not waterproof. The MMC is removable from Humminbird®
products, and can be used in a PC that is equipped with an appropriate card reader.
MMC is the same format that many digital cameras use. See SD.
