def asarrays(self):
        """
        Return *x* and *y* as arrays; their length will be the len of
        data added or *nmax*.
        """
        if self._ind<self._nmax:
            return self._xs[:self._ind], self._ys[:self._ind]
        ind = self._ind % self._nmax

        self._xa[:self._nmax-ind] = self._xs[ind:]
        self._xa[self._nmax-ind:] = self._xs[:ind]
        self._ya[:self._nmax-ind] = self._ys[ind:]
        self._ya[self._nmax-ind:] = self._ys[:ind]

        return self._xa, self._ya