-60% is the change from 255 to 102
Calculation steps:
[( 102 - 255 ) ÷ 255] x 100 = -60%
Formula
Percentage change = [(102 - 255) / 255] x 100
Subtract the new number by the original number
102 - 255 = -153
-153 ÷ 255 = -0.6
-0.6 x 100 = -60%
Example