-0.39% is the change from 256 to 255
Calculation steps:
[( 255 - 256 ) ÷ 256] x 100 = -0.39%
Formula
Percentage change = [(255 - 256) / 256] x 100
Subtract the new number by the original number
255 - 256 = -1
-1 ÷ 256 = -0.00390625
-0.00390625 x 100 = -0.39%