Calculate time elapsed from the point previously called
        this method or this object is created to this is called.

        Args:
            index (int): Index to be displayed, and be used to take intervals.

def add(self, index):
        """Calculate time elapsed from the point previously called
        this method or this object is created to this is called.

        Args:
            index (int): Index to be displayed, and be used to take intervals.

        """
        if (index - self.flush_at) < self.interval:
            return
        now = time.time()
        elapsed = now - self.lap
        elapsed_total = now - self.start
        it = index - self.flush_at
        self.lap = now
        if self.verbose:
            logger.info("iter={} {{{}}}={}[sec/{}iter] {}[sec]".format(
                index, self.name, elapsed, it, elapsed_total))
        if self.fd is not None:
            print("{} {} {} {}".format(index, elapsed,
                                       it, elapsed_total), file=self.fd)
        self.flush_at = index