12.5= square is 1/8 as dark as square D
25 = square is 1/4 as dark as square D
50 = square is 1/2 as dark as square D
100 = square is equally as dark as square D
200 = square is twice as dark as square D
400 = square is four times as dark as square D
800 = square is eight times as dark as square D
You may use any numbers, in between or more extreme than the above examples, to express your estimations of ratios of darkness.