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252 | Simrad MX500

GPS signals. See also GPS LOG.

TRUE HEADING

Direction in relation to true north. True heading is com-

pass heading corrected for MAGNETIC DEVIATION and

VARIATION. The true heading used by the navigator for

navigation calculations is a composite of magnetic head-

ing input from the NMEA compass, magnetic variation as

calculated by the navigator, and the values entered into

the compass deviation table.

TRUE NORTH

Direction along the meridian of the observer to the north

pole.

TRUE WIND ANGLE (TWA)

Similar to APPARENT WIND ANGLE, but compensated for

the motion of the vessel. TWA and AWA are equal if the

vessel is not moving.

TRUE WIND DIRECTION (TWD)

The direction of the wind over ground, expressed as an

angular distance from north clockwise through 360°.

TRUE WIND SPEED (TWS)

The wind speed relative to either ground or water rather

than to the moving vessel.

UNCERTAINTY

In the navigator, an indication of the expected accuracy

expressed as the radius of a circle around the calculated

(displayed) position. The uncertainty is expressed in

meters or feet. The calculation of uncertainty is based on

the HDOP value.

UNIVERSAL TIME COORDINATED (UTC)

Greenwich mean time corrected for polar motion of the

Earth and seasonal variation in the Earth’s rotation.

UPDATE

See POSITION UPDATE.

UTC

See UNIVERSAL TIME COORDINATED.

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Memorex RX 1 Smart Installationshandbuch Seite 253