'Format time-string: append the scale to the normal ISOT format.'

def format_string(self, str_fmt, **kwargs):

    time_str = super(TimeFITS, self).format_string(str_fmt, **kwargs)
    if (self._fits_scale and self._fits_realization):
        return u'{0}({1}({2}))'.format(time_str, self._fits_scale, self._fits_realization)
    else:
        return u'{0}({1})'.format(time_str, self._scale.upper())
