Monitoring observations of the CS (1←0) line near 26 GHz, covering more than a decade (from lower left to upper right). Channel spacings are (from the earliest to the latest epoch) 0.90, 2.7, 0.22, 0.90, 0.45, 0.34, 0.45, 0.42, 0.70, and 0.70 km s^-1. The ordinate denotes absorption in units of the entire continuum flux density of PKS 1830–211. The abscissa is local standard of rest velocity for redshift z = 0.88582.