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given angular rofafion of Vre prism SIbouf its
longitudinal asis causes the image to rotate
Ihmugh twice the angle. Also called rotating
prism.
draconic month—See nodlcal montrs.
drattlng gulda-See gulda.
drattlng-The arf of drawing from given
apacfflcetions.
drag-(lheodotile) A slight movemenl of the
graduafed ckcle of a fhaodolffe produced by lhe
tOtatlOn of the aikfade. See also atmosphetlc
drag.
drahtage pattern—The pattern or overall
aPPaafance made by the network of drainage
lealureS on a map or chart.
dralnag~ln mappirr~, all features associated
with waler, such as shorelines, rivers, lakes,
maretsea, etc.
drltt angle-(JCS) The angle measured in
degrees between the heading of an aircrall or
ship and the track made good. [Drift angle is
designated right or Iefl to indicate Ihe direction
of drfft.]
drltf station—A term sometimes usad in
ehoran operations to designate the ground
Stafion abouf which fhe aircraft flies during arc
navigation. The second ground station is fhen
referred fo as the rate atatlon.
drltt-1. (JCS) In ballistics, a shift in pmjecfile
direction due 10 gyroscopic actiin which resufts
from gravitational and atmospherically induced
Iorques on the spinning projectile. 2. The Iaferal
shift or dieplacemem of a ship or aircraft from tfs
course, Oue to the ac!”bn of wind or other
causea. 3. Aariaf photography obfained under
this wrrdffbn produces successive photographs
whose edges are parallel tit sidestepped. 4.
(precession) see total drift.
dummy pendulum—A pendulum of simifar
construti!on fo fhe workin~ pendulums excepf
thaf If }s equipped with a thermometer and is
fastened rigidfy in the receiver so that ii cannof
swing during observations. The dummy
perrdufum la eub]ect fo fhe same Iemparalure
cxsnditbrta aa fhe working pendufums, and k
used In deferminlng their temperature when In
use.
MIL-HDBK-850
dummy—1. A preliminary drawing or Ia.youf
showing the posltbn of ilkrafratiom and text as
fhey will appear in the final reproduct”bn. 2. A
set ot bfank pages mada up 10 chow the sire,
shape, and ~eneral style of a book, bc4det, or
pamphlet.
dumpy laval-A Ievefing instrument which has
its telascopa permanently attached to the
Ieve)ing base, effher rigidly or by a hinge thaf
can be manipulated by a micrometer screw,
duplex baaa-llne maaeurlrtg stpparatua—
A contacf base-line measuring apparafua,
composed of two disconnected bare, one oi
brass and the other of etaal, eac$r 5 maters &t
length and so arranged as to indicate the
accumulated difference of length of the
measures from the brass and steel
componams,
dupllcata Ieval llna-A Ikre of epiril leveling
composed of two airrgle lines run over fhe same
route, but in opposite directions, and using
different turning points.
dupllcate r?egat)w-(JCS) A negafive
reproduced from an orginal negative or
diaposilive. ~he duplicate negative may be a
fnre reproduction of the original or a
reproduction possessing greater or less contrast.
With dracf poaftiva materials, chemical reversal
process, and cfupfiiating film if is not atways
necessary fo maAe a posl!ke IO obtain a
duplicale negat}ve.]
DX-9D—An lMO/lHO proposed standard for the
exchange of digital data.
dyfux—A Iiiht-sensftiie papar or film usad for
proofing, usualfy has a bfue postfive reading
image wtth a blue background.
dynamic correction—The quantity that must
be added to fhe orfhomelric elevation of a poinf
to obtain ifs dynamic number.
dynamic elevaIlon—EIevation expressed in
Iengfh uniis, buf determined by dynamic
number.
dynamic gravity meter—A type of gravity
Instrument In wh’ch Ihe period of oscillation is a
function of gravity and is tha quamity directly
obae wed.
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