def _get_a3(bbar, dbar, slip_moment, mmax):
        """
        Returns the A3 term (III.4 in Table  4)
        """
        return ((dbar * (dbar - bbar)) / (bbar ** 2.)) * (slip_moment /
                                                          _scale_moment(mmax))
Returns the A3 term (III.4 in Table  4)