From the menu Tools → Image statistics

Show statistics about the pixel values in the current image.

This show the following:

• Min: The minimal value of a pixel.
• Max: The maximal value of a pixel.
• Mode: The mode of the image, i.e. the most frequent value. This is a good estimate of the sky background.
• Median The median value of the image.
• Mean: The mean value of all the pixel.
• Std.Dev: The standard deviation from the mean value.

If the image is plate solved the following values are added:

• Center RA2000: The J2000 right ascension of the image center.
• Center Dec2000: The J2000 declination of the image center.
• FOV: The image size width x height in minutes of arc.
• Image scale: The image scale in second of arc per pixel.