-84.06% is the change from 640 to 102
Calculation steps:
[( 102 - 640 ) ÷ 640] x 100 = -84.06%
Formula
Percentage change = [(102 - 640) / 640] x 100
Subtract the new number by the original number
102 - 640 = -538
-538 ÷ 640 = -0.840625
-0.840625 x 100 = -84.06%