-99.9% is the change from 990 to 1
Calculation steps:
[( 1 - 990 ) ÷ 990] x 100 = -99.9%
Formula
Percentage change = [(1 - 990) / 990] x 100
Subtract the new number by the original number
1 - 990 = -989
-989 ÷ 990 = -0.998989898989899
-0.998989898989899 x 100 = -99.9%