-39.05% is the change from 840 to 512
Calculation steps:
[( 512 - 840 ) ÷ 840] x 100 = -39.05%
Formula
Percentage change = [(512 - 840) / 840] x 100
Subtract the new number by the original number
512 - 840 = -328
-328 ÷ 840 = -0.3904761904761905
-0.3904761904761905 x 100 = -39.05%