def update(self, sensor, reading):
        """Update callback used by sensors to notify obervers of changes.

        Parameters
        ----------
        sensor : :class:`katcp.Sensor` object
            The sensor whose value has changed.
        reading : (timestamp, status, value) tuple
            Sensor reading as would be returned by sensor.read()

        """
        parents = list(self._child_to_parents[sensor])
        for parent in parents:
            self.recalculate(parent, (sensor,))
Update callback used by sensors to notify obervers of changes.

        Parameters
        ----------
        sensor : :class:`katcp.Sensor` object
            The sensor whose value has changed.
        reading : (timestamp, status, value) tuple
            Sensor reading as would be returned by sensor.read()