program:
  INT CONST x0 :: graphics x limit DIV 2;
  INT CONST y0 :: graphics y limit DIV 2;
  REAL CONST radius :: real (min (x0, y0) DIV 2);
  ask for starting point;
  enter graphics mode;
  heading;
  drive point along a circle;
  footing;
  sleep (5);
  enter text mode.

  ask for starting point:
    REAL VAR t;
    REP
      line;
      put ("Real number between 0.0 and 1.0: ");
      get (t)
    UNTIL 0.0 < t AND t < 1.0
    ENDREP.

  heading:
    put ("This program shows the cumulative effect of rounding errors.");
    line;
    put ("It multiplies a point on the unit circle repeatedly by itself").

  drive point along a circle:
    POINT VAR x :: point (t, sqrt (1.0 - t * t));
    REP
      picture point (x);
      x := x * x
    UNTIL abs (x) > 2.0 OR abs (x) < 0.5
    ENDREP.

  footing:
    move (1, graphics y limit - line height);
    put ("...until the point drops off the circle!").