'Get ERFA DUT arg = UT1 - UTC.  This getter takes optional jd1 and
jd2 args because it gets called that way when converting time scales.
If delta_ut1_utc is not yet set, this will interpolate them from the
the IERS table.'

def _get_delta_ut1_utc(self, jd1=None, jd2=None):

    if (not hasattr(self, u'_delta_ut1_utc')):
        from ..utils.iers import IERS_Auto
        iers_table = IERS_Auto.open()
        if (jd1 is None):
            self_utc = self.utc
            (jd1, jd2) = (self_utc.jd1, self_utc.jd2)
            scale = u'utc'
        else:
            scale = self.scale
        delta = iers_table.ut1_utc(jd1, jd2)
        if (scale == u'ut1'):
            (jd1_utc, jd2_utc) = erfa.ut1utc(jd1, jd2, delta)
            delta = iers_table.ut1_utc(jd1_utc, jd2_utc)
        self._set_delta_ut1_utc(delta)
    return self._delta_ut1_utc
