elevation above or below an adopted datum is
known. Usually designated as a BM, such a
mark is sometimes further qualified as a PBM
(permanent bench mark) or as a TBM (temporary
bench mark).
BILL OF MATERIALS—List of materials
needed for a given project placed directly above
the title block; not normally found on con-
struction drawings.
BISECT—To divide into two equal parts.
BITUMEN—A mixture of hydrocarbons of
natural or pyrogenous origin, or a combination
of both; frequently accompanied by nonmetallic
derivatives, which may be gaseous, liquid,
semisolid, or solid, and which are completely
soluble in carbon disulfide.
BLAST-FURNACE SLAG—The nonmetallic
product, consisting essentially of silicates and
aluminosilicates of lime and of other bases, which
is developed simultaneously with iron in a blast
furnace.
BLAZE—A mark made on the trunk of a
standing tree by chipping off a spot of bark with
an 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 inside
edge of the margin on a drawing.
BREAK LINES—Lines used to reduce the
graphic size of an object generally to conserve
paper 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 horizontal
line tangent to the upper surface of the centered
bubble, which lies in the vertical plane through
the longitudinal axis of the bubble tube.
CABINET PROJECTION—A single view of an
object having one face in orthographic projection
and depicting all three dimensions (length, width,
and height). The projection lines are parallel and
at an oblique angle with the plane of projection
(generally 45°). The lengths of the receding lines
are foreshortened to make the object appear
optically correct.
CALIBRATION—The determination in terms of
an adopted unit and by mechanical interpolation
based on the values obtained by standardization
of the supplementary marks on a measuring
instrument or device. Also, the determination of
the values of the divisions of a circle as
proportional parts of a circumference.
CAVALIER PROJECTION—A single view of an
object having one face in orthographic projection
and showing all three dimensions. The projection
lines are parallel and at an oblique angle with the
plane of projection (generally 45°). The lengths
of all object lines are drawn to scale and do not
appear optically correct.
CENTER LINES—Lines that indicate the center
of a circle, arc, or any symmetrical object; consist
of alternately long and short dashes evenly spaced.
CHAIN (Gunter’s)—A unit of distance formerly
much used in land measurement and a term
frequently found in deed descriptions. A chain
equals 66 ft, 4 rods, 1/80 mi.
CIRCLE—A plane closed figure having every
point on its circumference (perimeter) equidistant
from its center.
CIRCUIT CLOSURE—In leveling, the amount
by which the algebraic sum of the measured
differences of elevation around a circuit fails to
equal the theoretical closure, zero.
CIRCUMFERENCE—The length of a line that
forms a circle.
CIRCUMSCRIBED FIGURE—A figure that
completely encloses another figure.
CLOCKWISE ANGLE—A horizontal angle
measured from left to right. A clockwise angle
may have between 0° and 360°. Azimuths are
clockwise angles measured from either north or
south.
CLOSED TRAVERSE—A traverse that starts
and ends at the same point or at stations whose
positions have been determined by other surveys.
(See CONNECTING TRAVERSE and LOOP
TRAVERSE.)
AI-3
