-0.31% is the change from 645 to 643
Calculation steps:
[( 643 - 645 ) ÷ 645] x 100 = -0.31%
Formula
Percentage change = [(643 - 645) / 645] x 100
Subtract the new number by the original number
643 - 645 = -2
-2 ÷ 645 = -0.0031007751937984496
-0.0031007751937984496 x 100 = -0.31%