EQUILATERAL—A  polygon  with  sides  of  equal length. ERROR—The difference between an observed or computed value of a quantity and the true value of the quantity. Errors are of two classifications: accidental  errors  and  systematic  errors. ERROR  OF  CLOSURE—The  amount  by  which the  value  of  a  quantity  obtained  by  surveying operations  fails  to  agree  with  another  value  of  the same   quantity   held   fixed   from   earlier determinations or with a theoretical value of the quantity. EXPONENT—A small number or symbol placed above  and  to  the  right  of  a  mathematical  quantity to  indicate  the  number  of  times  the  quantity is  to  be  multiplied  by  itself;  for  example, EXTENSION LINES—Thin, unbroken lines used to  extend  dimensions  beyond  the  outline  of  a  view so  they  can  be  more  easily  read. FINITE   DISTANCE—A   defining   measurable distance. FIRST   ANGLE   PROJECTION—Multiview projection commonly used in Europe in which the top view is below the front view and the right side of the object, as shown in the front view, is toward the  left  side  view  of  the  object. FORESHORTENING—The  reduction  in  length of  receding  lines  in  an  oblique  projection  that allows the object to appear to be optically correct. FORESIGHT— 1. A sight on a new survey point, made in connection with its position determina- tion; or a sight on a previously established point to   close   a   circuit.   2.   In   leveling,   a   foresight (FS)  is  the  rod  reading  on  a  rod  held  on  a point whose elevation is being determined. (See BACKSIGHT.) FORMAT—The   systematic   arrangement   of drawing sheet space to  standardize  the  location of  required  information. FRACTION—A division indicated by placing the dividend  (numerator)  over  the  divisor  (denomi- nator) wit h a line between them. Proper   Fraction:   3/4 Improper  Fraction:  3/2  =  1  1/2 Mixed  Fraction:  1  7/8 FRENCH   CURVE—Instrument   used   to   draw smooth  irregular  curves. FREEHAND   DRAFTING—Any   drawing   in which the pen or pencil is guided solely by hand. FRUSTUM OF A CONE—The portion of a cone- shaped solid next to the base that is formed by cutting off the upper part by a plane parallel to the base. FRUSTUM   OF   A   PYRAMID—The   portion   of a pyramid-shaped solid next to the base that is formed by cutting off the top by a plane parallel to  the  base. FULL  SECTION—A  sectional  view  that  passes entirely  through  the  object. GEODETIC  DATUM—Datum  that  forms  the basis  for  the  computation  of  horizontal-control surveys in geodetic surveying. It consists of five quantities:  the  latitude  and  the  longitude  of  an initial point, the azimuth of a line from this point, and   two   constants   necessary   to   define   the terrestrial spheroid. GEOMETRY—That branch of mathematics that investigates the relations, properties, and measure- ment of solids, surfaces, lines, and angles; it also deals with the theory of space and of figures in space. GRADE (GRADIENT)—The rate of rise and fall or slope of a line; generally expressed in percent or  as  a  ratio. GRAPH  PAPER—Gridded  paper  in  a  variety  of scales and patterns used for plotting, sketching, and  drawing. GRID—A   network   composed   of   two   sets   of equidistant  parallel  lines  intersecting  at  right angles. GRID   COORDINATES—The   numbers   and letters  of  a  coordinate  system  that  designate  a point  on  a  grid. GUARD  STAKE—A  stake  driven  near  a  hub, usually sloped with the top of the guard stake over the  hub.  The  guard  stake  protects,  and  its markings  identify,  the  hub. AI-6