For optimal astro image viewing, adjust your screen brightness and contrast while carefully viewing all 20
squares and keeping the black surrounding as deep black as possible. Square No.1 should be indistinguisable
from the black background and it should be difficult to make out square No.2, while square No.3 should be
somewhat difficult. If you can't detect square No.3 at all, then your screen and/or viewing environment
are not optimised for astro image viewing, try dimming the lighting in your room.