def _parse_ergodic_cutoff(self):
        """Get a numeric value from the ergodic_cutoff input,
        which can be 'on' or 'off'.
        """
        ec_is_str = isinstance(self.ergodic_cutoff, str)
        if ec_is_str and self.ergodic_cutoff.lower() == 'on':
            if self.sliding_window:
                return 1.0 / self.lag_time
            else:
                return 1.0
        elif ec_is_str and self.ergodic_cutoff.lower() == 'off':
            return 0.0
        else:
            return self.ergodic_cutoff
Get a numeric value from the ergodic_cutoff input,
        which can be 'on' or 'off'.