-1.22% is the change from 820 to 810
Calculation steps:
[( 810 - 820 ) ÷ 820] x 100 = -1.22%
Formula
Percentage change = [(810 - 820) / 820] x 100
Subtract the new number by the original number
810 - 820 = -10
-10 ÷ 820 = -0.012195121951219513
-0.012195121951219513 x 100 = -1.22%