// Return zero if stored volume is zero
if (Scientific::equals([VST:m3], 0)) return 0.0;
// Return unit height if stored volume equals unit volume
if (Scientific::equals([VST:m3], [V:m3])) return [h:m] + [DC:m];
// Initialize
$d2 = [D:m] * [D:m];
$v = M_PI / 4 * $d2 * [h:m];
// Return analytical solution if fill height is within cylindrical section
if ([VST:m3] <= $v) {
  return 4 * [VST:m3] / (M_PI * $d2);
}
// Solve by Newton's rule
$x = [h:m] + [DC:m] / 2;
while (TRUE) {
  $h = $x - [h:m];
  $y = $v + M_PI / 3 * $h * (3 / 4 * $d2 - $h * $h) - [VST:m3];
  if (Scientific::equals($y, 0)) return $x;
  $x = $x - $y / (M_PI * ($d2 / 4 - $h * $h));
}

Calculates fill height by using Newton's method of successive approximations (Newton's rule).
Volume is only used to check the boundary condition at the beginning.