Version 2.0
213
Glossary
Operator’s Manual
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.
UTM
See UNIVERSAL TRANSVERSE MERCATOR.
UNIVERSAL TRANSVERSE MERCATOR
Alternative grid system used in harbor areas and for land applica-
tions instead of latitude and longitude.
VDL
VHF Data Link.
VDOP (Vertical Dilution of Precision)
An indicator of the accuracy in altitude. See DILUTION OF POSI-
TION.
Summary of Contents for MX420
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