docs: def _remove_observation_from_means(self, xj, yj):
          """Update the means without recalculating for the deletion of one observation."""
          self._mean_x_in_window = ((self.window_size * self._mean_x_in_window - xj) /
                                    (self.window_size - 1.0))
          self._mean_y_in_window = ((self.window_size * self._mean_y_in_window - yj) /
                                    (self.window_size - 1.0))