-0.9% is the change from 666 to 660
Calculation steps:
[( 660 - 666 ) ÷ 666] x 100 = -0.9%
Formula
Percentage change = [(660 - 666) / 666] x 100
Subtract the new number by the original number
660 - 666 = -6
-6 ÷ 666 = -0.009009009009009009
-0.009009009009009009 x 100 = -0.9%