-1.2% is the change from 830 to 820
Calculation steps:
[( 820 - 830 ) ÷ 830] x 100 = -1.2%
Formula
Percentage change = [(820 - 830) / 830] x 100
Subtract the new number by the original number
820 - 830 = -10
-10 ÷ 830 = -0.012048192771084338
-0.012048192771084338 x 100 = -1.2%