The red curve plots the solar intensity as a function of time. The detector is mounted in a fixed position, not necessarily vertical, so the intensity curve may not be symmetric about local noon. The blue curve plots the inverse of the scintillation amplitude, in volts RMS, so larger values imply better seeing. Note, however, that the scintillation reading is pretty strongly affected by clouds. When the intensity is varying rapidly, the scintillation data are certain to be of little use.
Previous plots are available in the archive.