elevation above or below an adopted datum isknown. Usually designated as a BM, such amark is sometimes further qualified as a PBM(permanent bench mark) or as a TBM (temporarybench mark).BILL OF MATERIALS—List of materialsneeded for a given project placed directly abovethe title block; not normally found on con-struction drawings.BISECT—To divide into two equal parts.BITUMEN—A mixture of hydrocarbons ofnatural or pyrogenous origin, or a combinationof both; frequently accompanied by nonmetallicderivatives, which may be gaseous, liquid,semisolid, or solid, and which are completelysoluble in carbon disulfide.BLAST-FURNACE SLAG—The nonmetallicproduct, consisting essentially of silicates andaluminosilicates of lime and of other bases, whichis developed simultaneously with iron in a blastfurnace.BLAZE—A mark made on the trunk of astanding tree by chipping off a spot of bark withan axe. It is used to indicate a trail, a boundary,location for a road, a tree to be cut, and so on.BORDER LINES—Dark lines defining the insideedge of the margin on a drawing.BREAK LINES—Lines used to reduce thegraphic size of an object generally to conservepaper space. There are two types.Long—Thin ruled line with freehand zigzag.Short—Thick, wavy freehand line.BROKEN SECTION—See partial section.BUBBLE AXIS (LEVEL VIAL)—The horizontalline tangent to the upper surface of the centeredbubble, which lies in the vertical plane throughthe longitudinal axis of the bubble tube.CABINET PROJECTION—A single view of anobject having one face in orthographic projectionand depicting all three dimensions (length, width,and height). The projection lines are parallel andat an oblique angle with the plane of projection(generally 45°). The lengths of the receding linesare foreshortened to make the object appearoptically correct.CALIBRATION—The determination in terms ofan adopted unit and by mechanical interpolationbased on the values obtained by standardizationof the supplementary marks on a measuringinstrument or device. Also, the determination ofthe values of the divisions of a circle asproportional parts of a circumference.CAVALIER PROJECTION—A single view of anobject having one face in orthographic projectionand showing all three dimensions. The projectionlines are parallel and at an oblique angle with theplane of projection (generally 45°). The lengthsof all object lines are drawn to scale and do notappear optically correct.CENTER LINES—Lines that indicate the centerof a circle, arc, or any symmetrical object; consistof alternately long and short dashes evenly spaced.CHAIN (Gunter’s)—A unit of distance formerlymuch used in land measurement and a termfrequently found in deed descriptions. A chainequals 66 ft, 4 rods, 1/80 mi.CIRCLE—A plane closed figure having everypoint on its circumference (perimeter) equidistantfrom its center.CIRCUIT CLOSURE—In leveling, the amountby which the algebraic sum of the measureddifferences of elevation around a circuit fails toequal the theoretical closure, zero.CIRCUMFERENCE—The length of a line thatforms a circle.CIRCUMSCRIBED FIGURE—A figure thatcompletely encloses another figure.CLOCKWISE ANGLE—A horizontal anglemeasured from left to right. A clockwise anglemay have between 0° and 360°. Azimuths areclockwise angles measured from either north orsouth.CLOSED TRAVERSE—A traverse that startsand ends at the same point or at stations whosepositions have been determined by other surveys.(See CONNECTING TRAVERSE and LOOPTRAVERSE.)AI-3
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