-60.16% is the change from 640 to 255
Calculation steps:
[( 255 - 640 ) ÷ 640] x 100 = -60.16%
Formula
Percentage change = [(255 - 640) / 640] x 100
Subtract the new number by the original number
255 - 640 = -385
-385 ÷ 640 = -0.6015625
-0.6015625 x 100 = -60.16%