def internal_to_external_delta(self, internal_value, internal_delta):
        """
        Transform an interval from the internal to the external reference (through the transformation). It is useful
        if you have for example a confidence interval in internal reference and you want to transform it to the
        external reference

        :param interval_value: value in internal reference
        :param internal_delta: delta in internal reference
        :return: value and delta in external reference
        """

        external_value = self.transformation.backward(internal_value)
        bound_internal = internal_value + internal_delta
        bound_external = self.transformation.backward(bound_internal)
        external_delta = bound_external - external_value

        return external_value, external_delta