// 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 [D:m];
// Solve by Newton's rule
$x = [D:m] / 2;
while (TRUE) {
  $y = M_PI * $x * $x * ([D:m] / 2 - $x / 3) - [VST:m3];
  if (Scientific::equals($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).
Volume is only used to check the boundary condition at the beginning.