/* Return zero if stored volume is zero */
if (Scientific::equals([VFL:m3], 0)) return 0.0;
/* Return unit height if stored volume equals unit volume */
if (Scientific::equals([VFL:m3], [V:m3])) return [D:m];
/* Solve by Newton's rule */
$x = [D:m]/2;
while (TRUE) {
  $y = M_PI*$x*$x*([D:m]/2-$x/3)-[VFL:m3];
  if (Scientific::equals($y, 0)) return $x;
  $x = $x-$y/(M_PI*$x*([D:m]-$x));
}

Calculates fill height by using Newton's method of successive approximations (Newton's rule).