moving radar:
  enter graphics mode;
  print heading;
  determine parameters;
  draw moving radar;
  wait for confirmation (2 * graphics x limit DIV 3, 1);
  leave graphics mode.

print heading:
  put ("Moving radar");
  line;
  put ("============");
  line.
  
determine parameters:
  REAL VAR radius :: ask real ("Radius? ");
  radius := min (radius, real (min (graphics y limit, graphics x limit)) / 2.1);
  put ("Radius used: ");
  put (text (int (radius), 3));
  REAL CONST step x :: min (1.0, real (graphics x limit) / 360.0);
  REAL VAR centre x :: max (0.0, radius - 260.0);
  INT CONST centre y :: graphics y limit - int (radius).

draw moving radar:
  INT VAR i;
  FOR i FROM 0 UPTO 360
  REP
    move (round (centre x), centre y);
    draw (round (centre x + aspect * sin (i) * radius), centre y + round (cos (i) * radius));
    centre x INCR step x
  ENDREP.