Differences in β and dispersion functions of the SSRF storage ring with the undulator off and on. The tunes and chromaticities are adjusted to the same values and no other errors are included. The absence of vertical dispersion generated by the undulator shows that the undulator does not generate coupling between the horizontal and the vertical planes. In principle, the β-beating generated by the undulator can be largely corrected using the adjacent quadrupoles. The figures at the bottom show that this level of disturbance does not affect the beam dynamics significantly.