-0.12% is the change from 821 to 820
Calculation steps:
[( 820 - 821 ) ÷ 821] x 100 = -0.12%
Formula
Percentage change = [(820 - 821) / 821] x 100
Subtract the new number by the original number
820 - 821 = -1
-1 ÷ 821 = -0.001218026796589525
-0.001218026796589525 x 100 = -0.12%