Image to image difference. Difference between two images shot within a minute of one another with identical camera settings and no post processing changes. In theory, there should be no difference thus demonstrating that stuff happens (light changes, etc?) over time.
Image #4 which should also show no differences - if NX perfectly cancelled the effect of an in-camera setting - shows "different differences" than here in #5.
4 which is a comparison of two versions of the same captured image - versions altered by an NX Base Adjustment - is much cleaner (less "noisy") than here with #5. The differences in #4 are *solely* in those portions of the images impacted by the differing treatments of sharpening between the camera and NX.
#5, on the other hand, differs throughout and is dominated by a "noisy" granular effect that is due to the difference between two completely different captures and not the camera vs NX effects within the same image.