def max_temperature(self,  unit='kelvin'):
        """Returns a tuple containing the max value in the temperature
        series preceeded by its timestamp
        
        :param unit: the unit of measure for the temperature values. May be
            among: '*kelvin*' (default), '*celsius*' or '*fahrenheit*'
        :type unit: str
        :returns: a tuple
        :raises: ValueError when invalid values are provided for the unit of
            measure or the measurement series is empty
        """
        if unit not in ('kelvin', 'celsius', 'fahrenheit'):
            raise ValueError("Invalid value for parameter 'unit'")
        maximum = max(self._purge_none_samples(self.temperature_series()),
                   key=itemgetter(1))
        if unit == 'kelvin':
            result = maximum
        if unit == 'celsius':
            result = (maximum[0], temputils.kelvin_to_celsius(maximum[1]))
        if unit == 'fahrenheit':
            result = (maximum[0], temputils.kelvin_to_fahrenheit(maximum[1]))
        return result
Returns a tuple containing the max value in the temperature
        series preceeded by its timestamp
        
        :param unit: the unit of measure for the temperature values. May be
            among: '*kelvin*' (default), '*celsius*' or '*fahrenheit*'
        :type unit: str
        :returns: a tuple
        :raises: ValueError when invalid values are provided for the unit of
            measure or the measurement series is empty