LEVEL SURFACE—A surface that is parallelwith the spheroidal surface of the earth, such asa body of still water.LEVELING—The operations of measuringvertical distances, directly or indirectly, todetermine elevations.LINE OF SIGHT—1. The straight line betweentwo points. This line is in the direction of a greatcircle, but it does not follow the curvature of theearth. 2. The line extending from an instrumentalong which distant objects are seen when viewedwith a telescope or other sighting device.LINE OF SYMMETRY—A line that divides anobject into two equal identical parts; used onlywhen the two halves of an object are identical.LIQUID LIMIT—The upper limit of the plasticstate, expressed as the moisture content at whichthe flow curve intersects the “25 blows” ordinate.LOGARITHM—The exponent or the power towhich a fixed number, called the base, must beraised to produce a given number; for example,common logLOOP TRAVERSE—A closed traverse that startsand ends at the same station.MAGNETIC AZIMUTH—An azimuth measuredwith reference to the direction indicated by amagnetic compass needle. Magnetic azimuth ismeasured from magnetic north, which is east orwest of true north, as shown by the magneticdeclination.MAGNETIC DECLINATION—The angularamount that a magnetic compass needle pointseastward or westward from true north.MAP MEASURE—Instrument used when lengthsof irregular outlines are measured.MATCH LINES—Lines used when an object istoo large to fit on a single drawing sheet and mustbe continued on another sheet. The points wherethe object stops on one sheet and continueson the next sheet must be identified withcorresponding match lines. They are mediumweight lines indicated with the words match lineand referenced to the sheet that has the cor-responding match line.MATHEMATICS—The science that deals withthe relationships that exist between quantities andoperations, and with methods by which theserelationships can be applied to determineunknown quantities from given or measured data.MEAN SEA LEVEL—The average height of thesea for all stages of the tide. Mean sea level atnumerous tide-gaging stations usually forms thebasis of a level datum for large areas.MEASURED ANGLES—Angles that are eithervertical or horizontal.MECHANICAL DRAFTING—Any drawing inwhich the pen or pencil is guided by a mechanicaldevice.MERIDIAN—A north-south line from whichlongitudes (or departures) and azimuths arereckoned.MIDPOINT—That point on the arc of a circularcurve that is the same distance from both endsof the arc.MILITARY STANDARDS (MIL-STDs)—Instructions set forth by the Department ofDefense that members of all armed services arerequired to follow. Only a few of these standardsrefer directly to drafting.MINUTE—A 60th part of a degree used to definethe size of an angle.MOISTURE CONTENT (w.)—The ratio,expressed as a percentage, of the weight of waterin a given soil mass to the weight of solid particles.MONUMENT—Any object or collection ofobjects that indicates the position on the groundof a survey station. In military surveys, the termmonument usually refers to a stone or concretestation marker containing a special bronze plateon which the exact station point is marked.NONCIRCULAR CURVE—A curve composedof a series of extremely small circular arcs ofvarying radii.NON-NORMAL LINE—A line that is oblique toone or more of the planes of projection.AI-9
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