@staticmethod
def _actual_ofreq(ifreq, ftw, rsize):
    """Return the actual output frequency.
        Due to the resolution of the DDS, the actual output frequency
        may be (a bit) different than the queried.
        :param ftw: Frequency Tuning Word register value (int).
        :param rsize: Size of register (int).
        :returns: Actual output frequency (float).
        """
    return ftw * ifreq / (1 << rsize)
