CUBE—Rectangular solid figure in which all six faces are square. CUTTING  PLANE  LINES—Thick,  heavy  lines used  to  indicate  a  plane  or  planes  in  which  a sectional view is taken. CYLINDER—A   solid   figure   with   two   equal circular bases. DATUM—Any numerical or geometrical quantity that   serves   as   a   reference   or   base   for   other quantities.  It  is  described  by  such  names  as geodetic,   leveling,   North   American,   or   tidal datum,   depending   upon   its   purpose   when established. DATUM  LINES—Dark  medium  lines  consisting of one long and two short dashes evenly spaced; used  to  define  a  line  or  plane  of  reference. DECIMAL—The result of dividing the numerator (top  number)  of  a  fraction  by  the  denominator (bottom   number);   for   example,   1/2   =   .5, 3/8  =  .375,  17/100  =  .17. DECLINATION—The  angle  between  true  north and  either  grid  or  magnetic  north. DEFLECTION   ANGLE—A   horizontal   angle measured from the prolongation of the preceding line, clockwise or counterclockwise as necessary, to  the  following  line. DEGREE—A 360th part of the circumference of a circle; also, a 360th part of a revolution about a  point;  used  to  define  the  size  of  an  angle. DEPARTURE—In  a  plane  survey,  the  amount that one end of a line is east or west of the other end. The plane coordinates of a point are known as the casting and northing of the point, and the departure is the difference between the castings of the two ends of the line, which may be either plus  or  minus. DESIGN  MANUALS  (DMs)—Publications  con- taining guidelines set forth by the Naval Facilities Engineering  Command. DETAIL  PAPER—Heavy  opaque,  buff,  or neutral green drawing paper that takes pencil well. DIAGONAL—A   line   that   connects   any   two nonadjacent  corners  of  a  plane  figure. DIAMETER—A  straight  line  passing  through  the center of a circle or sphere whose ends terminate at  the  circumference  or  surface. DIMENSION   LINE—A   thin,   unbroken   line (except in the case of structural drafting) with each end terminating with an arrowhead; used to define the   dimensions   of   an   object.   Dimensions   are placed  above  the  line  except  in  structural  drafting where the line is broken and the dimension placed in the break. DIRECT   LEVELING—The   determination   of differences of elevation by means of a continuous series of short horizontal lines. Vertical distances from  these  lines  to  adjacent  ground  marks  are determined by direct observations on graduated rods with a leveling instrument equipped with a spirit level. DIRECT   READING—The   reading   of   the horizontal  or  vertical  circle  of  a  theodolite  or engineer transit with the telescope direct. DISCREPANCY—1.   The   difference   between duplicate or comparable measures of a quantity. 2.  The  difference  between  computed  values  of  a quantity  obtained  by  different  processes  in  the same survey. DISPLAY  CHART—Chart  used  to  convey  data to  nontechnical  audiences. DIVIDERS—Instrument   used   to   transfer distances. DRAFTING   MEDIA—Materials   used   to   draw on. Basically, three types are used: paper, cloth, and  film. EASTING—One of the two values indicating the position of a point on a grid system. The casting coordinate  is  abbreviated  E. ELEVATION—The  vertical  distance  of  a  point above  or  below  a  reference  surface,  or  level datum;  often  abbreviated  ELEV. ELLIPSE—A plane closed curve having the sum of  the  distances  from  any  point  on  the  curve  to two  fixed  points  a  constant. ENGINEER’S  SCALE—A  scale  used  whenever dimensions are in feet and decimal parts of a foot, or  when  the  scale  ratio  is  a  multiple  of  10. AI-5