Estimated Position Error (EPE) A calculation that indicates the potential position inaccuracythe user may experience due to a variety of GPS factors which include satellite position in the sky, signal strength, and others factors.

Fix Type Indicates whether the GPS receiver is providing 2D fix or 3D fix. A 2D fix requires only three satellitesand provides only latitude and longitude. A 3D fix requires four or more satellites,and provideslatitude,longitude, and altitude.

GPS (Global Positioning System) GPS provides accurate position (latitude, longitude, altitude) information virtually anywhere on the earth through satellite technology and personal receiverson the ground. See How GPS Works.

Heading 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 travelingin a slightly different direction than it is heading, and therefore Heading is often confused with Course Over Ground. See Course Over Ground.

Map Datum Refers to a particular survey of the earth’ssurface that was referencedwhen creating a chart (i.e. WGS84).It is important to select the correct Map Datumsetting in your fishfinder when comparing GPS position to a paper chart to avoid slight position inaccuracies.Almost all electroniccharts use the WGS84 Map Datum and therefore, they do not require setting changes.

MMC (Multi Media Card) An MMC is a postage stamp-sized memory device used to store electronicdata such a maps, waypoints, routes, and other information. MMC is a very rugged format suitable for the marine environment, but it is not waterproof. MMC is the same format that many digital cameras use. See SD.

North, Magnetic 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 variationsin the earth’s magnetic field around the globe, the difference betweenTrueNorth and MagneticNorth can be greaterthan 10°. See True North.

North, True 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 TrueNorth as the setting. The GPS heading may vary from the boat compass heading because the compass uses Magnetic North. See

Magnetic North.

Glossary - GPS & Navigation Terms

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