This button will open a popup-window which shows some image statistics (see Fig. 5.18) for the unzoomed (original) and zoomed (displayed) image. If you have marked a region (rectangle) on the image, the statistics for that will be displayed as well (zoomed and unzoomed).
Displayed are the number of pixels in X and Y as well as the
total, the mean value, the total (integrated pixel values for the
whole image), the minimum and maximum along with their position,
the variance, standard and absolute deviation, skewness and
kurtosis
. For the definition of those values check the IDL
help for the MOMENT function.