def calculate_speed(self, section, alignment_results=None):
        """ Calculate speed using alignment information.

        :param section: The section (template or complement) we're calculating
            speed for.
        :param alignment_results: Optional dictionary of the alignment summary,
            so that speed can be calculated without having to write the summary
            out to the fast5 file first.
        :return: Speed in bases per second or zero if the speed could not be
            calculated.

        The only reliable way we have of finding out how many bases have gone through the pore is by
        looking at how much of the reference the sequence aligned to. This takes that information and
        uses it to calculate speed in reference-bases-per-second.
        """
        speed = 0.0
        if alignment_results:
            results = self._get_results(alignment_results)
        else:
            results = self.get_results()[section]
        if results['status'] != 'match found':
            return 0.0
        ref_span = results['ref_span']
        ref_len = ref_span[1] - ref_span[0]
        seq_span = results['seq_span']
        seq_len = seq_span[1] - seq_span[0]
        total_len = results['seq_len']

        sample_rate = self.handle.get_channel_info()['sampling_rate']

        # We need the duration from the segmentation results
        chain = self.handle.get_chain(self.group_name)
        if chain is not None:
            segmentation_group = dict(chain).get('segmentation')
        else:
            segmentation_group = None
        duration = 0
        if segmentation_group is not None:
            with SegmentationTools(self.handle, group_name=segmentation_group) as seg:
                summary = seg.get_results()
                if summary is not None:
                    duration = summary['duration_{}'.format(section)]
        if duration == 0:
            return 0.0

        normalized_duration = duration * seq_len / float(total_len)
        speed = sample_rate * ref_len / normalized_duration
        return speed
Calculate speed using alignment information.

        :param section: The section (template or complement) we're calculating
            speed for.
        :param alignment_results: Optional dictionary of the alignment summary,
            so that speed can be calculated without having to write the summary
            out to the fast5 file first.
        :return: Speed in bases per second or zero if the speed could not be
            calculated.

        The only reliable way we have of finding out how many bases have gone through the pore is by
        looking at how much of the reference the sequence aligned to. This takes that information and
        uses it to calculate speed in reference-bases-per-second.