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Appendix I, Continued
MEAN TIME.—Time based upon the
rotation of Earth relative to the mean Sun.
MERCATOR PROJECTION.—A
conformal cylindrical map projection in
which the surface of a sphere or spheroid,
such as Earth, is conceived as developed
on a cylinder tangent along the equator.
MERIDIAN.—A north-south reference
line, particularly a great circle through the
geographic poles of Earth.
MESSAGE.—Any thought briefly stated in
plain or secret language in a form suitable
for rapid transmission.
METER.—The basic unit of length of the
metric system, equal to the distance at 0°C
between two lines on a standard
platinum-iridium bar.
MICROSECOND.—One-millionth of a
second.
MILLIBARS.—A unit of measure of
atmospheric pressure.
MINUTE.—The sixtieth part of a degree of
arc.
MODULATOR.—That part of radio
equipment that alters the amplitude,
frequency, or phase of a radio signal in
accordance with speech or a signal, or that
regulates the length of a pulse.
MORSE CODE.—Dots and dashes used in
communications in place of letters,
numerals, and punctuation.
MRM.—Distance of relative movement.
The distance along the relative movement
line between any two specified points or
time.
NAUTICAL ALMANAC.—A periodical
publication of astronomical statistics useful
to, and designed primarily for, marine
navigation, particularly the American
Nautical Almanac published by the U.S.
Naval Observatory.
NAUTICAL
ASTRONOMY.—Navigational astronomy.
NAUTICAL MILE.—A unit of distance
used principally in navigation. See Knot.
NAVIGATION.—The process of directing
the movement of a craft from one point to
another.
NEAP TIDES.—The tides occurring near
the times of first and last quarter of the
moon when the range of tide tends to
decrease.
NIMBOSTRATUS.—A dark, low,
shapeless cloud layer (mean upper level
below 6,500 feet), usually nearly uniform;
the typical rain cloud.
NOMOGRAM.—A diagram showing to
scale the relationship between several
variables in such a manner that the value
of one that corresponds to known values of
the others can be determined graphically.
NOT UNDER COMMAND.—A ship
disabled or uncontrollable.
AI-8
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