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length equetton—A condillon equation
whkt! expresses the relatbnship between
the flxad kanglha of Iwo lines whch are
connected by triangulation.
length 01 degrea-The length of a degree
of Iatfiude measured along a meridian or
tonglfude. The IerrQth varies somewhat wiifr
the degrees of Ialttude. Those near the
pole are longer and those near the Equator
are efrorler. The tengsh also varies WMI
different selections of sphemlds.
level controf-A aerles of bench marks or
other points of known elevation,
established throughout a project.
level correction—That correction which is
applied to an observed difference of
elevation tO correct for the error imroduced
by the lacf that the line of sight through the
Ieveting instrument is not absolutely
horizontal when the bubble is centered in
its vial. Sea atso Ieval constent., ., .
level Nne-1. A line on a level surface;
therefore a curved fine, 2. A tine over which
bVeling operations are aCCornplished. See
also dupllcete level Ime; ltne of
levels; multtple level Ilne:
slmulteneoua level Ilne; epur Ilne of
Ievela.
Ievet nel—See eurvey net, detlnition 2.
level rod-See Ievellng rOd.
lev~~r~eu:~ce—See equlpotentlal
Ievet trier-An apparatue for use in
measuring the angular value o? the
divlsbna of a apiriI level,
Ievellng error of cloeure—See error of
closure, definition 4.
leveling lnatrument—An Instrument used
tor determining dltferences 01 elevations
between points, See also Abney level;
dumpy level; Egault level;
enslneer”a level; firel.order level;
Flacher Ieval; Gravett level; hand
MIL-HDBK-850
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level; hanging level; Iet}tude Ieval;
Lenoir level; Iocator’a hand level;
mllltary level; pendulum level; plate
level; praclaa level; reverelble level;
●alf-levellng level; ●plrlt level;
Stampfer level; ●trldlng tavel;
teleecope level; tlttlng Ieval;
Troughton level; U.S. Geological
Survey level; wye [Y) Iavel.
Ievallng rod-A straight md or bar, deelgned
for use in measuri~ a vertical distance
between a potnt on tha gruund and the line
01 collimatbn of a leveling instrument which
has been adjusted to a horizorrfat posttlon.
Also called bvel rod; rod, See aleo
Barlow Ievellng rod; Boaton Ievellng
rod; double-target leVellng rod;
foot-meter rOd; Gravatt Ievellng rOd;
Invar Ievellng rod; long rod; Molltor
praclsa Ievellng rod; New York
Ievellng rod; Pemberton Ievellng
rod; Phlledelphla Ievellng rod;
preclsa Ievellrrg rod; range rod; salt.
raadlng Ievellng rod; ahorf rod;
alngle-target leveling rod;
Stephenson Ievellng rod; tepe rod;
targat Ievetlng rod; U.S. Englnear
praclsa Ievellng rod; U.S.
Geological Survey precise Ievellng
rod.
leveling the model—See Ievellng,
detinilion 2.
line map-See planlmetrlc map.
line of apsldas—Tha major axis of an
elliptical orbit extended indeflmtely in Lmth
directions. Also called apse Ilne.
Ilne of collimation—(oplics) The line
through the second nodal palm of the
Objedive lens of a telescope id the center
of Ihe reticla. Aleo called almlrrg tlna;
fine of eight: polntlng Ilne; ●lght
Ilne.
Ilne of constant trcale-Any line on a
photograph wtrich is parallel to the trve
horison or 10 the ieomatric psrallel. Also
called Ilne ot equal acala.
Ilne of equal acala-See Ilne of