def METHOD_NAME(self, source: Source) -> tuple[str | None, str]:
    """Return the attribute of the source entities that is used to measure the value, and its type.
    For example, when using Jira as source for user story points, the points of user stories (the source entities)
    are summed to arrive at the total number of user story points.
    """
    source_type = self.sources_dict[source["source_uuid"]]["type"]
    entity_type = self.__data_model["sources"][source_type]["entities"].get(self.type(), {})
    attribute = entity_type.get("measured_attribute")
    measured_attribute = None if attribute is None else str(attribute)
    attribute_type = self._get_measured_attribute_type(entity_type, measured_attribute)
    return measured_attribute, attribute_type