/* 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];
/* Return if stored volume is invalid */
if ([VFL:m3] > [V:m3]) return NULL;
/* Solve by Newton's rule */
$x = [D:m]/2;
while (TRUE) {
  $y = [L:m]*([D:m]*[D:m]/4*acos(1-2*$x/[D:m])-([D:m]/2-$x)*sqrt(([D:m]-$x)*$x))-[VFL:m3];
  if (Scientific::equals($y, 0)) return $x;
  $x = $x-$y/(2*[L:m]*sqrt(([D:m]-$x)*$x));
}

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