A plot of the focus of the various guide probes, together with a best fit line. If the line is roughly horizontal then the telescope is in good focus. Clearly more needs to be said about how to use this plot to estimate the best focus, but I don't yet have that information.
This plot always shows data from the most recent guider image (even if the guider window is displaying some other image, e.g. from its history). If that guider image contains no data for the guide stars then the plot is be blank.
Note: the best-fit "line" is a curve because it is actually a straight-line fit to FWHM squared.
